Fret life is pretty hard to quantify in terms of hours. String type, action and technique play a pretty big role. Also, different set-ups and styles of music/tone requirments will tolerate more or less fret wear.
There's a guy in my town that has matching 68 Precision and Jazz basses. He is physically the quietest bassist I've ever seen, nothing moves except his fingers, and only a little. His basses are strung with flats and have been since he got the basses "new" in the early 70's. I understand they were in the back room of a mom and pop music store tucked away. You can tell they've been played but the basses are 100% original and the frets are almost perfect. If I strung one of his basses with rounds, tuned-it down a half step/set-it up the way I liked I would probably cause more wear in two weeks than he has in 30 years.
I agree with g-tarded, initially superficial wear is more visible on a fanfretted bass. I actually think that over the long haul the frets will last longer because the string crossing the fret at more or less than perpendicular means the string is contacting a slightly larger surface area of the fret, but this is just a silly little theory of mine.
Ultimately wearing out frets means that your getting your money's worth out of an instrument, and that's a good thing.