It does make Necrons tougher to batteries. The 4+ saves were so that they would be roughly as well defended as shielded ships.
They do take a hit to armor, but only -1, so 5+ rather than 4+ armor. However, if they attempt to repair criticals, thats also -1 to armor, so could still get down to 4+ armor. I felt Necrons needed some more durability, as they are the most advanced race, yet their light cruisers and smaller had paltry defenses compared to similar sized ships of other races. Also, its a well known fact that Necron ships, on average, are grossly overpriced for what they bring to the table. The only reason I can assume is ability to focus the entirety of their firepower.
Right now what is ruminating in my head is the weapons loadout. Gauss Whips are localized currently in the 'DINF'. The intent was to have a bit more general firepower at the expense of less focusable firepower, to keep a necron ship from completely pwning another ship into the dust.
I did this because the key things necrons are known for is their durability. Their firepower is potent, but I personally found all that focusable nastyness very Eldar-like, and I wanted the feel of the necrons to be different than their mortal enemies.
So my question is, is focusable firepower something people feel is 'right' for necrons? Is the fleet missing something by lacking the ability to pour firepower onto one ship? Is it missing something with the limitations on what gets a star pulse?