Just picking out a few points of your post. Gossip Girl and The Playboy Club did not air at the same time. Gossip Girl airs at 8 I believe and the The Playboy Club was on at 10. The CW only programs from 8-10, instead of 8-11 like ABC,NBC, and CBS. Also, I don't think the four big networks are paying much attention to what the CW airs at anytime, the CW's ratings are no better than many cable networks. Also Fox only broadcasts until 10 as well, which means Animation Domination ends at 10 and Pan Am starts at 10 so they are not competing. Also Animation Domination only performs very well when it airs after football, most of the time its ratings are only slightly above average (with Family Guy really being the only hit).
The reasons Mondays are so competitive I believe is because it is the start of the week. All of the networks want to have a big show on Monday so that they can promote the rest of their shows that will air during the week. So it is an important night for the broadcast channels. I also don't think anyone expected Two and Half Men to be as big at is after the premier. It has not dropped off as sharply as expected, but it is still decreasing each week, and after another month or so it is possible it will no longer be a massive hit.
For Terra Nova specifically Fox is very competitive on Sundays-Thursdays. X-Factor takes up most of Wednesdays and Thursdays. Tuesday is the day for Glee and their two comedies. Sunday is animation. They weren't going to air Terra Nova on Friday, so that only left them with Mondays.







