I think the reason many do that; is people don't care about tier 7 or 8 anymore. Pretty much it comes down to tier 9 being purchasable by emblems which can be farmed in heroics. Now 25 man t9 isn't, so that would still pose an upgrade, even to pre-raid chars who had only hit 5 mans so far.
Actually, unless Blizzard has stronger quest rewards comming out in Cataclysm, I see an interesting thing comming. Basically it amounts to this. HFP quest greens were a fair upgrade over classic gear. People were replacing their raid gear with them, and some complained.
So the result was that Howling and Borean quest rewards were utterly pathetic. TBH, I don't really bother doing the questson alts for gear anymore. I'd rather just join up with achievement runs through TBC raids, and if lucky get some of the gear out of BT, Hyjal, etc. I really can't be bothered questing for such week rewards this last expansion provided, and tbh with already 4 80s, and way more 70s (from the last expansion then I'd care to count) I'm kinda bored questing in general anyhow. I'm not far off from lore master and the 3,000 quest achievement on one of those 80s anyhow. Now throw a PvP realm into the mix; ya know, getting ganked doing quests I'm bored of already, for rather week rewards that can't even measure up to kara level gear is bleh. And when guildies or even PuGs go after a kara achi (if they even need it, well DKs can); they're typically doing a 2 or 3 man gold run anyhow; as simply put they don't need more to clear it now.
So where does this leave things in Cataclysm? Well one can farm heroics for straight out tier 9 and iLvl 232 epic gear. What one can't get there, they can get through ICC 5 mans. I well imagine that if Cata greens aren't stronger people with their alts will skip the nub zones altogether, lvl farming WotLK 5 man heroics, use the emblems to buy t9; and won't bother touching the new content till after they have it.
Many people, and I'm comming closer and closer to that, have taken to questing less and lvling through instances rather more; after having had so many lvled chars anyhow. Dailies too have lost some interest due to, well again there's only so many days one can do the exact same quest before it's like "next"