I don't think it was intended for people to use a mix of 10-man and 25-man gear for a BiS list, it just worked out that way. Sticking with the different iLevels of gear, the alternative would be to have the same items re-used, but labeled 10-man/10-man heroic/25-man/25-man heroic. That gets clunky really fast.
There's also the annoyance that comes with explaining that, yes, it's a tier or two back in content, but it's still BIS for my class/spec. Right up there with explaining why I was using a couple resilience pieces in BC as a feral druid.
It was still vastly more interesting though. Now, you literally always just grab whatever drops and is for your role, unless you already have the better version. And that sucks.
The best system, imo, gives a much wider selection of items (with no reforging) and gives the potential for interesting stat interplay that makes the value of each truly relative to your other stats even in the context of a single gear tier
A few classes still get some interesting gear choices (mainly kitties), but that's because their only task is to keep their stats about equal.
I would be hesistant to say it wasn't intended. Perhaps that's true, but it certainly wasn't unwanted on Blizz's part, considering how long it took them to introduce gear pieces with proper stats to stop it. If they had just failed to do so for one tier, it would be one thing, but this went on for 3 expansions (well, 2, but I didn't know what to call Vanilla :P).
Realistically, Cata was just a significant change in gear philosophy. Edited, Jul 13th 2011 6:31pm by idiggory