First..."friends" is a subjective term. To those who rely on deep, in-person contact it's not likely that they would describe online friends as actual friends, but to the person with mostly online friends they find those relationships to be qualifying friendships. So...po-tay-toe, po-tah-to.
Myself being a person with a good number of in-person friendships and having been a player in the MU community for years, I can say that I wouldn't describe many of my "Mu community friendships as actual friendships.
I can only think of a small number of times where crossing from text to voice wasn't an absolute nightmare. I think most "MU friends" are best described as "Acquaintances who symbiotically need each other's presence to validate their hobby and online social life who want to keep rules on how and when the acquaintanceship crosses over into the real world; they will likely not follow you to the real world should you choose to leave the hobby."
Just being frank, here. While a number of the people in the hobby are friendly with each other, be it to gossip or roleplay or TS or to assume mutual defense to keep creepers or shitty roleplayers out...the vast majority of them wouldn't drive chicken soup to your house if you were on your deathbed. The majority will not want you to have access to their home, spouses, or children. The people here are predominantly strangers to each other and while there are exclusions to every concept...the "friendship" boundary is placed on involvement in the hobby.
Which, to me, is not a friendship.