Coz I'm a flash bastard with more money than sense...
Lol - on a more serious note, it's because I'm in the middle of writing the second edition of DJing for Dummies - the main reason for the second edition being that I want to put more info in there about digital DJing.
As Traktor and Serato seem to be the market leaders in terms of vinyl control of MP3's, it made sense to get them both. It's not really a comparison thing, more a function thing for what kind of DJ might use them.
FWIW - I really like Serato because it's so basic - just tunes playing and that's about it. But, the four decks and the added effects section on Traktor Scratch Pro leads me to keep that connected most of the time.
(Plus, I find more clubs have a Serato installation already, so all I need to do is rock up with my laptop and vinyl, and I'm off. More and more places have the ability to hot swap in with Traktor though, so I always carry the Audio 8 with me just in case)
Success is merely a failure to imagine more