I've seen it with lesbians and straight girls. Maybe they do it because guys like it. I always thought the whole lesbian thing to be some stupid stereotype man thing untill I saw some of my college girlfriends kissing at a party, I thought it was really hot.
In europe everyone kisses everyone else as a greeting, on the cheeks or on the lips, it's just a peck though not a snog. This dosn't happen so much in england, mostly family and close friends. I've kissed one guy with tounges, it's just like kising a girl, but he didn't have a beard.