Tobold seems to be suggesting that raids are not as profitable as quests and heroics, due to drawing in a much smaller audience. As my own observation, on top of that raids, since they are intended to be challenging, not just bigger, balance is much more important, requiring that much more effort. Does your average solo questing player care much about class balance? Probably not. But your average raider, they are going to care, they must care.
What would WoW be with no raids?
I have to admit, I can't quite imagine it. Would we have progressively more difficulty 5-mans and heroics? We've never quite seen that. Magister's Terrace and the three sneak attacks on Icecrown Citadel bumped things up but a tier or two, but even Halls of Reflection didn't exactly strike me as content that people would spend much time on. The gear requirements were a bit higher, but only a bit.
On the other hand, it does fit the trend. Raids have gotten progressively smaller. BC took them down to 25. LK made 10 man raids almost an alternative path to 25. Now Cataclysm has made 10 into a small version of the 25, with the same gear and shared lockouts. Could we see raids gone altogether, or dropped down to 10 man and 5 man?
Maybe not. Maybe Cataclysm and the focus on strengthening guilds is an attempt to rebuild the focus on raiding and raid sizes and challenges could even climb again.
On the other hand*, beside changes to raiding there has been the trend of progressive casualization or accessibilityization or whatever other made-up word you can think up to express a poorly-defined concept. This suggests that the trend could continue and that the emphasis on guilds is only to offset the negative side-effects of teaching us to be asocial bastards, with no actual goal.
I'm probably looking at this all wrong, to suggest that with no raids WoW would go on the path of challenging 5-mans. More likely with no raids we'd just see trivial 5-mans, slightly less trivial 5-mans, and a whole lot of very slow grinds, with only the smallest shred of an economy or player community. In other words, pretty much just the current WoW but with no raids.
* This is why President Truman infamously cut off one hand from every economist he hired. The man was brutal.