Who said they are? I'd argue they're trying to do the opposite. Yes, across the board, all stats should matter. But they shouldn't matter equally to everyone. In fact I doubt there's a class that has no clear stat priority one way or the other. They actually explicitly stated this:
Originally Posted by Blizzard Entertainment
Inside Hellfire Citadel, you’ll see a wider range of high and low secondary stat values on items than you have in a long time. Alongside some tuning adjustments that should ensure your attuned stats are the right choice, this change should also make it easier for you to identify which items are good for you in a more interesting way than just “equip the highest Item Level.” Our goal is to help make Hellfire Citadel Raid items more distinct and meaningful to you, and we hope you’ll let us know how things feel once you start collecting your new gear.
I don't see why you'd say that. A raid isn't meant to be just plain 'hard' or just plain 'easy'. Boss difficulty has always varied from very easy to very hard, relative to each other, at least, within the same tier. The easier bosses come first, which actually makes complete sense, otherwise players would be hitting a brick wall before they even start. Let's say hypothetically, the boss difficulty ranges from 1-4 on normal, 4-7 on heroic and 7-10 (inclusive) on mythic. So the easiest group of bosses would be 1/4/7 out of 10 on N/H/M, and so forth with the last boss being a 4/7/10 out of 10 on N/H/M. A 1-10 scale makes the overlaps pretty awkward, and makes it impossible to rank certain bosses without decimals, but just go with it, for the sake of simplicity. So this means the 'average' boss difficulty for a normal raid (assuming 4+4+4+1 boss distribution, as far as difficulty is concerned) would be about 2.15 out of 10, which does actually make sense. Now this isn't to say that all bosses with a boss difficulty of ~2 together make up the 'normal' difficulty. It just means that all bosses of that difficulty should drop more or less the same ilvl, because a non-specific group that is able to beat one of them shouldn't have many problems beating most.
And don't misquote me on this with specific iLvl and boss ranks in HFC, the numbers I chose are completely arbitrary. In the simplest terms: Just because two bosses are equally difficult doesn't mean they belong in the same difficulty, especially if they're entry level vs. end level bosses (eg. Boss 1 & Boss 9).
This builds on what I already brought up - not all bosses in the same raid difficulty are meant to be equally difficult, nor are they meant to be beaten at the same item level. But a group that is able to clear ~40% of a raid should have the skill it takes to complete it, but may struggle due to a lack of gear (iLvl), provided they don't overgear it in the first place. So if <Guild A> is able to clear HFC normal with little difficulty, they should have the skill necessary to beat a few bosses on HFC heroic with some difficulty. At the same time, players who easily clear the first half of HFC heroic shouldn't run into too many problems clearing the rest of it. And if they do, within weeks of upgrading their gear, they'll be able to push through even that. This isn't new to HFC, it's how it's always been. HFC just goes a step further with this by having the drop in iLvl steadily increase - which isn't to say that by the time you reach Boss 10 you'll have overgeared the encounter already. While a lack of proper balance can lead to this, more than anything it means that the climb in difficulty would be steeper. So where you previously saw bosses ranked 1-4 in a 4+4+4+1 instance (3-winged, +final boss), we may be now seeing a 1-5 or even 1-5.5 difficulty range. Again, the 1-10 scale makes it a bit awkward, but I think you're getting my point.