As a New Yorker, I'd have to agree. There already seems to be a glut of taxis for most times of the day (in addition to the higher-end sedans that very few people use).
Arecibo (car service) almost always arrives within 5 minutes, and on numerous occasions I've had them say "ok, they're downstairs already" while still on the phone with them.
Not really a problem in need of solving in NYC, although it certainly will be interesting to see how it is received here.
Plus I'm sure the car services are going to be resistant to the fees associated with it, changing their work flow, and are thinking about all the income I'm sure they don't declare. Actually, I just remembered this article from a while back about the car services: http://nymag.com/news/features/54678/
But sure, maybe someday I'll tap a screen to take care of it once we hit a quorum of use, I have no opposition to it. It just doesn't seem to be a problem in my life that needs solving. Yet another third party trying to get in between the transaction to skim some money off.