Going back to the original post, I wouldn't say "dating" normally implies monogamy. Personally, I've found it's very easy for me to fall into being monogamous with someone I'm very interested in, much as Ron described above. However, experience has taught me to always assume that a guy is continuing to sleep with other people until or unless we both decide otherwise. As such, I'm now trying to appreciate the benefits of being single... but it's sometimes tough when you're surrounded by couples.
As for why not go straight to second base, I think the reason things are the way they are is because our community at large still holds on to a lot of unfortunate taboos about sexual behavior, inherited from heterosexuals. There's still this overwhelming assumption (both from those we "date" and from the community at large) that if we make a sexual connection with someone first (i.e., a "hookup"), it says something negative about them or means a deeper relationship isn't possible. So, gay men feel forced to play these silly games where both parties try not to seem too "easy", and to downplay their sexual history/activity.
Of course, those aren't absolutes. A lot of men out there truly do prefer an emotional connection before having sex with someone. What's sad is that both types of sexual personalities aren't accepted. I think this narrow-mindedness on the part of our community (ironic as it is) may share a large part of the blame for the dishonesty, cheating, etc. that we see.