Forced grouping is a terrible model. It's also a very bad idea to restrict solo ability to one or two classes. Scrappers, for example, are boring to play, and I'd be sorry if solo ability were only restricted to them.
I can sort of see making grouping *advantageous*, but beyond that I don't get. I did the forced grouping thing for 5 years in EQ, and I will never do it again.
And no, playing Morrowind or something is not the same. There are many levels of sociality between Morrowind or some single-player game, and the forced grouping model most MMOGs seem to impose these days. The more I'm forced to group, the less I'll play.
