First, Halo 3 sells over $170 million its first day.

Secondly, Halo 3 players would also be interested in UT3.

Unreal Championship 2 came out in April 05. Halo 2 came out in November 04. Couple months difference for great games in the same genre. One story I've heard is Epic was aiming for the '04 holiday season, but realising that Halo 2 was coming out around the same time, delayed the game's release, using the time to polish it more and give it a fighting chance at making money. The holidays are competitive enough as is, seeing more games released in from September through December than the rest of the year. Good titles can easily get overshadowed by blockbuster, AAA-budget games with their AAA-marketing budgets. So supposedly UC2 got bumped to avoid Halo 2 and the glut of other titles.

If that's true, then its possible Epic is repeating that. IGN's Gamermetrics (according to the the Gamasutra article) believes that Halo 3 and UT3 share customers. Not a great leap there. It also doesn't require rocket-science to know that given Halo 2's performance that MS would be pushing it hard (in fact, its easily verifiable). I could be wrong (and maybe Shacks can correct me), but I can't think of a single PS3 FPS that would be likened to Halo 3 in terms of sheer hype and marketing, giving Epic and UT3 a more commanding presence. Similarly, the PC is where Unreal is an 800 lb. gorilla, so its hard to picture there being much to challenge them there.

While timed exclusivity does make sense (ie, Sony paid for the lead), its possible that Epic played a shrewd hand; have Sony pay for what they would've done anyhow. I suspect the truth will only ever be known by Mark Rein and company, though.