The only SC lances have come from BL books with bad editors. I think it is to a point of: they really don't care. What is worse: letting such a thing slip or simply don't care enough?
And yes, Marines can do a pin point orbital attack: They call in the Nova or a Venerable Battle Barge with lances.
Since the fluff war won't be won due heavy entrenchments I call this:
Why on earth give Marines lances from a game balance point of view: NONE AT ALL.
Planetstrike isn't a BL book, it's a GW 40k expansion rulebook. So, your assertion that it only comes from BL books is untrue. (One would hope the editing standards are higher)
As far as why SM need lances: As many people have complained: BC use the gunnery table. Lances do not. All hail the blast marker.
Since the largest thing the sensors can pick out is a WE and can't fire into point on the map, I'd gather from that there is some reason why the lance batteries are unable to pick out coordinates and can only target object. It's not spelled out, but the lack of being able to input a set of coordinates to target like you do with the battery barrages seems to indicate the lance targeting systems work in a different and incompatible method. It could have something to do with the batteries affecting an area of space and targeting a set of coordinates while the lances lock onto and track objects. It's just not explained and could be any number of reasons.
Except that the old Damocles command rhino fluff describes it working exactly that way, feeding information to orbiting starships from the SM commander. Since it also states that they use it for heavy support 'as a last resort...reserved for the most dangerous of foes...' I would state that it's almost a textbook example of it.
There's not a lot of fancy footwork. just look at all the described sources and then look at what you posted from planetstrike. Planet strike is the odd man out. BTW, isn't that quote you just posted in reference to the Black Legion or Nightlords controlled ship? That would put it outside the realm of this discussion and could very well be retrofitted with lances. It's just not clear if the covenant is the strike cruiser or if it is a chaos vessel capable of intercepting the strike cruiser.
The
Covenant of Blood is a NL strike cruiser. It and it's sister SC
Excoriator, apparently of the same class, are both lance fitted SCs that predate the heresy. Most of
Soulhunter and
Throne of Lies take place aboard her. Granted, outside of our discussion, except that it's implied that the NL 10th company have not even taken the time to recruit new members since the heresy, let alone refit the ship, some sections of it becoming dangerous due to lack of repair and refit.
There is an interesting commentary on the difference in time, for the crew of
Covenant of Blood it's only been a hundred years or so since the Heresy, despite it having been 10,000 for the galaxy.
Regardless of newer fluff in relation to possible lances being right or wrong, there is one thing that NOTHING you've posted can refute: standard pattern Strike Cruisers are not equipped with lances. We know this because the fluff is in the BFG books and that both epic and bfg do not equip lances on marine vessels by default. If lances do exist on strike cruisers, they are very rare because all the fluff references you post still refer to just a handful of ship compared to thousands controlled by the Marines. Now from a gameplay perspective, we know people like lances and tend to take them when they can so to make sure these lances stay rare on strike cruisers there are only a few ways to do this. First you can set a limit (0-1) which isn't very good because it makes the upgrade better at low point games and worse at high point games. You can also limit them by ratio which we have now and scales to high or low point games. None of those discourage people from taking as many as they can though, so upping the cost to be less competitive remains to keep the lances rare since most people will avoid them.
A chapter can have a maximum of 10 Strike cruisers. Given that there are supposedly 1000 chapters, this means that there are approx 10,000 loyalist SCs in existence, give or take. However, variants would not be even throughout the chapters, due to individual chapters favoring differing combat doctrines. Chapters such as the Minotaurs would favor boarding torps and thawks, as they primarily engage in anti-ship operations and close assaults, where as a chapter known for it's precision strikes might favor lances and teleporters.
I do not disagree that the lance is NOT the standard pattern of SC. What I disagree with is the instance that they do not exist at all, when there is plenty of evidence to the contrary. I feel that the requirement that half of all the SC MUST be the standard type accurately reflects this, but also allows more variety in SCs. I would also limit SC to no more then 10 total, as this is the max any one chapter CAN field, with the possible exception of the BTs, as fluff also states that each company has it's own SC.
However, I might also point out that, at least in the example in Planetstrike, the chapter in question has three of them. Which would match up with the HA's requirement of one normal SC for every variant, as this would mean that about 1/3 of the entire chapters SC are fitted with lances.
Further, as far as your assertion about the targeting ability of lances: the old Damocles command rhino fluff describes it working exactly that way, feeding information to orbiting starships from the SM commander. Since it also states that they use it for heavy support 'as a last resort...reserved for the most dangerous of foes...' I would state that it's almost a textbook example of it. I would suggest that the scatter in 40k the 40k version is due to them calling coordinates rather then locking on to a single target. It's not that it can't, it's that it isn't as accurate.
As long as a hit is rolled, the max scatter is only about 20 feet to scale in 40k. The lances in 40k, despite assertions to the contrary, do, apparently suffer attenuation, being only a Str 10 ap1 hit when fired from orbit, but a str D ap 1 hit when fired from the ground at a target. (See defense laser stats for apoc by GW)