Anecdotal support; Uber is keeping me from purchasing a car. I have an inexpensive motorcycle that handles 95% of my rapid transportation needs, and I try to live in areas where walking or mass transportation solve my "slow transportation" needs. I use Uber for all the edge cases where walking or motorcycling doesn't cut it, and I cannot see any scenario where I'd prefer to own a car and drive myself compared to the ease and reliability I have experienced with the service so far. Maybe Uber won't be the king of the hill when the dust settles, but so-called "ride sharing" services absolutely are taking dollars that would otherwise go into purchasing a vehicle, a much larger market.
Important to note you haven't given up vehicle ownership though. You just haven't switched types of ownership. Uber needs to be more than your 5% edge cases if we're talking about disrupting ownership habits.
Bill Gurley's post is very interesting and in-depth. One thing he doesn't mention is the potential of UberPool(combining multiple passenger trips into a single car) to further increase demand. I wonder why is that ?
http://fivethirtyeight.com/features/uber-isnt-worth-17-billi...
His basic assumption was to use the taxi market as the total addressable market (TAM)
Bill Gurley, a VC from Benchmark and one of the investors in Uber, lays out alternative scenarios for TAM including going after car ownership. http://abovethecrowd.com/2014/07/11/how-to-miss-by-a-mile-an...
Damodaran's response to Gurley concedes its probable/plausible/possible for uber to get into non-Taxi and larger markets: http://aswathdamodaran.blogspot.in/2014/07/possible-plausibl...
Bottom line: the optionality of uber going into these larger markets is what is driving these valuations