Well, yes, from one point of view you're definitely right. This can be one of the major downfalls of total-immersion roleplaying, if you're looking for that kind of deep friendship with people where you share everything going on in life. There are so many things you might want to share and yet never have a chance to do so.

I've had some friendships which went from total immersion to real life friends where we even traveled to visit each other. Once our characters became such fantastic friends, we both thought that maybe we could be friends in real life too, and so (obviously) broke the total-immersion rule we were following at the time.

Some other friendships seem perfectly natural and normal when they're kept in character all the time -- both people have some kind of unspoken agreement that this is how they enjoy spending time together. While it's true that it never goes "deeper" than that in the sense of sharing real things from life, there's also something special about knowing you can roleplay with that person any time they're online without having to talk about all the frustrations of life as well. You can sort of put those aside for a while and just have a nice time. Not every good relationship has to be "deep" in the same way.

Anyway, so there are some exceptions to various norms and things which mean that sometimes total-immersion can really work for people. Othertimes, yes, there are drawbacks, but for whatever reason people are willing to deal with those. It all depends on who people are and what they want out of the experience of the moment -- sometimes that changes over time too, and it's okay. I myself have drifted between total-immersion some times, and hardly any roleplaying at all at others.