Since the announcement last year at Blizzcon that several stats would disappear in Cataclysm, players have been asking questions. As it is right now gear is fairly linear (by gear level) but does manage to have several "side grades" that allow players that understand the math behind the stats to fiddle with gear and get more out of it that other players that do not understand the mechanics.
These players are quite concerned that the simplification system will make gear always a direct replacement if it is a higher item level, making replacement uninteresting and not requiring any knowledge or though process. Blizzard had this to say in the forums about it.
I think you're approaching it as a player, in which your goal is to improve your character as much as you can as fast as you can. From that viewpoint, any piece of loot that isn't an unambiguous upgrade just gets in your way. But think for a moment about the over-arcing design of loot in the game and the role it fills. Deciding what is an upgrade is part of the challenge in the same way figuring out to beat the boss is part of the challenge. The hit stat represents a gearing challenge because you can't just assume any loot from Icecrown is an automatic upgrade. It may be a huge upgrade. It may be a sidegrade. It may be a slight upgrade, but only if you swap around a couple of other pieces, consider regemming, etc.
In short, you have to game it.
Put another way, even if there is a "best in slot" list for every spec, the order in which you get those pieces is significant, and makes you have to think and solve problems. That's why I call hit "interesting." Spellpower, while quite desirable, is not interesting in that more is always better to the extent that we can't even offer variation on it from one piece to the next any longer. The rating-based stats, especially those with caps as low as hit, cause you have to solve the puzzle in order to wear them. There aren't a lot of huge decisions you make in WoW, beyond perhaps your class and maybe your guild. But there are a lot of little decisions that when taken together make the game fairly compelling.
Too often players approach gear design as "I would never wear that piece, therefore it's a badly designed piece." But consider for a moment that badge vendor +hit trinket again. It might not be attractive to you personally assuming you're hit capped in your current gear. Your conclusion might be that the trinket was itemized wrong. But that might not be the conclusion of say a Resto druid who decides to try Balance and now has a huge hit deficit to overcome. Regemming or farming old content is one way to do it, but relatively slow and / or painful. Getting a shiny new trinket off a vendor (i.e. isn't even subject to the whims of boss loot RNG) with a whole bucket of +hit on it starts to look pretty attractive. Just because the piece isn't for you doesn't mean it isn't filling a gap in the fabric of the game.
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