What they call a lance (surgical strike) in 40k could/would be completely different from what they'd call them in BFG. Don't forget, lance/WB are classes of weaponry, not specific names for weaponry. And if something like a Tau railgun is a WB then I'm sure WBs can be used for precision orbital strikes. Hell, a different ammo round or cohesion focal point or energy input could produce this effect, depending on the weapon.
I imagine WBs acting like a projectile weapon for the most part, where you have to calculate the intersection between the round and the target. A lance on the other hand would be much more like the weaponry in Babylon 5, ie, scything through space.
According to 'current' fluff, a weapon battery fills a volume of space with fire, though aiming is involved. Older WBs seem to be composed of lasers, while newer are solid projectiles. Some have increased range due to gravimetric manipulation (grav culverins) or refined propellants (turbo weapons). Plasma weapons are also considered wbs, and would be terminally disrupted by a planets EM field, as a plasma bolt is a electromagnetic package surrounding a chunk of plasma. Tau may very well be able to use railguns through an atmosphere, as an ion bolt would not penetrate for the same reasons as a plasma round.
Ancient targeting systems fluff has been revised, and, if converted to BFG, would be a left shift rather then the extension to range on most IN ships.
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Lure of the Expanse from FFG has a nice illustration of a lance strike on a building by a Firestorm, for those questioning what a lance strike looks like as fire support.
And, much to my irritation, GW has officially condoned FFGs work as the current fluff for our beloved ships, which is why the HA is having such a hard time getting ships changed/approved.
