PS3 is even a better media streamer for home theater. With certain apps (Windows or Mac) you could stream any video format into it.
Granted, PSN movie and music library is total suck compared to iTunes (PSN is a 90% games store anyway), and Apple TV consume less energy than PS3, but the hassle of downloading content and only play Apple exclusive movie/music format on it is a let-down. No HDD, no optical drive (yes, optical .. something Apple fanboys would hate because Steve said so)
Plus, your PS3 has built in bluray player .. That's 10x better than iTunes' so-called HD movies, better resolution, clarity, superb sound and all. Nothing can beat the physical media quality yet unless today's home internet can download or stream 50GB of data under 2 hours. iTunes' movies is no more than MKV files you found on torrent, bundled with

logo on it, and called as legal movies
Really, no reason for buy Apple TV if you already have ps3. iPad video stream to HDTV .. 99% gimmick. Although this is a Mac forum, and I'm a Mac user, still I'd like to keep things objective.