That's how it seems to me, too. I wrote erotic fiction for this site long before I ever even thought of RP, so I view RP as an extension of that hobby. The development of characters and plots when more than one person is contributing is the entire of allure of RP to me, so I vastly prefer first-person, playing a distinctly different role each time.
There is the standard trap of the character becoming you rather than you becoming the character. I've heard that said to be one of the problems with first-person perspective in literature, and I can't imagine it being any less of a problem in RP.