We know a bit more about Michael solely because , as a contract player, he's had more screen time. I feel they've been purposely "holding back" on the development of Liam because they want him to have this "unattainable" quality that would drive Fallon to extremes. The less we know about him, the more likely it is we'll like him (since unflattering aspects of his personality have been kept from us). That big blow-up between Michael and Fallon in this episode allowed them to finally talk about the events that sank their engagement, but having them go right back to bed seemed like the writers did not "really" want them to work out their differences like adults and learn from their failed relationship. Mature adults, I think, would have come to realize that they're better off not romantically involved--because she is so screwed up, and because he doesn't want to be "Mr. Fallon Carrington". I think Michael was fine with being 'the chauffeur having sex with the boss's daughter' but now that he's discovered his own ambitions, he's more likely to want a woman who can support his efforts and put him first--neither of which describes Fallon.
(or to leave)
