There are thousands of them and they're separated into different instrument tracks. They even had bands re-record songs sometimes where seperate masters couldn't be found. If I recall correctly, Third Eye Blind did this for Semi-Charmed Life.
I'm happier that it's a (mostly) open standard, but I'm still slightly annoyed at the confusion that comes from NI appropriating the industry term. It's like if I released a non-text representation of storing data using a particular subset of technology that was standardized, and then called it "The Binary" format. Technically nothing wrong with it, but it's bound to cause confusion!
Ideally, I'd have liked to have seen a completely open audio codec used for both encoding and container, but MP4 is a pretty safe bet for compatibility , and it's not really NI's fault that it has some patent issues.
All in all, I could pedantically argue the "open" status, but I'll instead give credit where it's due, and give kudos to NI for releasing a pretty damn usable file format.
I'm even happy that it's limited to 4 parts. For the purposes of live performance with DJ style gear, this is plenty. If a performer wants more parts then they're probably going to be creating some or all of those parts. Either way, they'll probably be using something more like Ableton rather than Traktor.