I think we should just adopt the wait-and-see philosophy here.

Agree'd that 10 people taking down a formerly 40 man boss is a little wacky, but there have always been cases of less taking down something designed for more (hell look at classic hunter solo'ing or the DK that solo'd sarth!). True this is more of an off the radar kinda playstyle, but in the lore of the realm i think the news would spread about that badass that spanked the dragon all by himself.

I have faith in Blizz for the raiding future. I think the ruby sanctum will be a good indicator for how things will go in cata. From the screenshots i've seen it seems populated with foliage, which i think is a good way to get around some of the spatial issues in raids, create a certain amount of ground clutter. In 10m more people will follow the strait path, whereas in 25m a few people walk on the other side of the tree's etc etc. now it seems spread out in 25m and condenced in 10m, hopefully making them even.

As to fighting the boss themselves and asking how 10 people took down a former 40m boss? Well sheesh how did the lich die anyways? Shouldnt we have to destroy his Phylactery? or was that in a quest i missed. How is it Onyxia doesnt just fill the room with fire EVERY time instead of when a player tries to bug her out of her room? Why doesnt Kologarn wait untill your looking over the edge of the cliff to say peekaboo? etc etc. There is always going to be a wtf was this boss thinking kinda deal. and there is always gonna be a how are we killing him kinda deal. "Oh really? Yea the guy who raised an entire continent of undead. Yea he killed his father.... yea it took about 15 minutes. Well Tirion was there!.... No he didnt really do alot till the end. But he was there!!"