Some people say they like yuri because it feels more emotional and less shallow, but I think yuri has an issue with being too much one way or the other. In more traditional yuri, aimed at women, it can very often come across as "pure to the point of sterility", where the main object is nebulous things like "wanting to hold hands" as opposed to any physical desire to consummate love. In that respect it really
does feel like a "romantic friendship", where the two girls might very well be happy living out their whole lives together without so much as a kiss.
And then you have the other extreme, more often found in series aimed at men, where the "predatory lesbian" can often reign supreme. That's why I have to sort of chuckle about the previous post about how "oversexed" male homosexuals come across on TV shows, when anime has the same problem when it comes to predatory lesbian groping or leering in the place of what a man might prefer to do.
This, of course, excludes the rare series written by and for lesbians, which tend to be very balanced...and utterly unread by those that aren't lesbians. (Well, I'm not a lesbian, and I enjoy that sort of yuri, but...)
I'm not trying to claim that BL is a bastion of realism (because "lol, just...no"), but I think you more often find a little more of a mixture between the dramatic passionate relationship coupled with a strong physical attraction. You'd have to go back to the seventies to find a series where two guys from a "shounen ai" series are content with holding hands and mooning at one another. And, likewise, if a guy is canon gay in a BL series, you don't see endless scenes of him grabbing another guy's junk or nosebleeding in the locker room--even though his attraction will be obviously manifest.
BL also has a stronger range of genres and subjects it covers, whereas yuri seems regulated to the "boarding school ghetto", mainly because of the pervading notion that persists to this day that the only reason a girl could be attracted to another girl is because there are no men around. The girl's sexuality is still orbiting around men, it's just that she was treated cruelly by them and seeks "immature" solace with another woman. At least BL deals with the concept of girlfriends and societal disapproval, even if it's in the most general sense of "but we're two guys".
As a final note,
anyone who is crowing about the superiority of yuri in terms of depth of quiet, subtle emotion should go read "Kinou Nani Tabeta" right now.
