Lynata said:
The power armour in BoM is closer to carapace than Marine armour, which is a direct contradiction to the current Codex. Dark Heresy was not written by Games Workshop but by Black Industries, and just like the Black Library novels and comics they are but interpretations that do not necessarily compare to studio canon. It is also worth pointing out that, back when Black Industries still had the license, Space Marine power armour had AP8 and Astartes boltguns did 2d10 damage. Just something to note, perhaps, but that fits much better to the actual Codex descriptions than what DW has right now.
The same type of contradiction the whole DW book currently is? 
Pulse rifles do less damage than a bolter right now. The Codex speaks quitea different language.
Actually, according to GW, all stuff written using the GW IP, regardless of the source, is, due to it being vetted and approved by GW, and are entirely 100% canon. There is no difference in "canon level" between stuff written by GW, and stuff written by Black Library writers, FFG, Sabretooth Games (the guys who make the TCGs of the GW IP settings), etc.
So saying "it's different in the tabletop rules" isn't actually a rebuttal to the assertion that Space Marine armour and weaponry is better than other models of the same weapons, even those used by the Sisters of Battle, as the tabletop game is an abstract of the setting made to fit with d6s being used for everything, and as such is going to be less accurate because of said abstraction.
Even pointing out bits in fluff that say that it's the same isn't a true rebuttal, since GW also say that none of the fluff is 100% correct - some are lies, some are personal opinion of the person writing it, some of it is propaganda, and some of it are half-truths. Just because the Witchhunter Codex (which is now 2 editions out-of-date, and is in serious need of an update) says that Sisters of Battle are just as well equipped as Space Marines doesn't mean that it is so.
All Non-GW fluff is 100% canon with itself. It MAY contrdict another novel/book/even GW product.
The only product free of any personal shift are the codex rules. Space marine and IG statlines have been unchanged since the 3rd edition, with a very low chance of being changed anytime soon.
FFG has a chance to provide euqally untainted and comparable rules for equipment. But they have failed quite a bit, since even power levels qre quite a bit off sometimes (see pulse weapons)