Uber doesn't have to put taxis out of business, it's growing the market - getting a lot more people using taxi-like services. Both people who aren't willing to shell out how much cabs charge in their artificially restricted markets and people who've had shitty experiences with cabs in the past. Not to mention how poor taxi service is in the vast majority of US cities.

I personally use Uber because I hate calling a cab company, finding out it does or doesn't have a cab to send, figuring out the address I need it to come to, getting a very general estimate of when it'll be there (8-15 minutes), etc. With uber I drop the pin in the exact spot I want it, I know the minute my cab is there. If cab companies had an app like that, they'd have my business.