You're right that it was a good decision for sony. I believe it was a poor decision for Epic. The PC/PS3 sales are so clearly (to me) going to cannibalize the 360 sales which will be crap for this game. The same way Elder Scrolls Oblivion being out on 360/PC for a year killed any chance at great sales for it on PS3. Sega's poor decision to release virtua fighter 5 on the 360 months later resulted in terrible sales on both systems in the end.
Epic may be repeating Sega's blunder by releasing a game that is going to be overlooked on the PS3 during the holidays. Then releasing it in like May or sometime on 360 which will also sell like crap by then since few will care by then. It'll result in PC - Good sales, PS3 - poor-average sales, 360-poor sales. Then Epic will be crying that console owners don't buy good PC games as an excuse.