There is no user-agent detection between any models on iOS in Safari; it's not an oversight. You've never been able to detect a difference between iPad 1. 2, 3, 4 or 2(mini) or iPhone 3, 3GS, 4 and 5, nor should you. User agent detection is horrible and this isn't news.
Downloads over iTunesD show difference though; since you may want to serve them different payloads. "iTunes-iPad/5.1.1 (4; 16GB; dt:77)" vs. "iTunes-iPad-M/6.0.1 (2; 64GB; dt:75)"