Build-specific loot

I was in a great raid last night, where my guild performed significantly better and faster in Naxxramas-10 than before, and we managed to kill 10 bosses in 4 hours. But I was a bit annoyed about the loot. Not just that of 22 epics I ended up not getting a single one, that was just bad luck. But about us having to shard several epics because they were specific to a single build of a single class, and nobody needing them in the raid.

In our case we had neither holy paladins nor resto shamans in the raid, and of course got lots of drops with plate and mail armor with +spellpower. If we had had a tankadin or enhancement shaman, he might have gotten the epic for "off spec", but we had no paladins nor shamans at all, so the epics ended up sharded. And that in a raid group where lots of people were wearing blues and could well have used some Naxxramas epics.

What did strike me was the contrast with some other epics we found, for example a ring with intellect, stamina, and spellpower. Half the raid needed that. And I also noticed that while some builds and classes do have specific raid loot, that only they can use, other builds of other classes have absolutly nothing specific for them. Healing power has been removed from the game, so the typical cloth armor piece my priest could use is typically needed as well by all the mages and warlocks, not to mention priests of every other build. I refrain from rolling need on items with +spell hit, but dps casters don't necessarily refuse rolling for cloth armor just because it has spirit or mana regeneration on it.

So I'm wondering why Blizzard designed it that way. Wouldn't it be better if either every class / build had specific loot to avoid too many people fighting over it; or if every piece of loot was useable by several classes and builds. If Blizzard can combine healing power and spellpower in one, then why not combine other stats in one as well, so that no class / build has loot that is only useable by them?