I agree that people prefer a sense of ownership rather than renting, even if renting is in their best interest.

However, the problem with a one-time payment is that the vendor loses incentive to continue supporting the buyer after the transaction. The primary way to generate additional revenues from that customer is, as you say "sell new innovations and features".

This adding of new features can increase complexity which eventually impacts the ease of use and increases the learning curve. These two side effects can have a negative impact on new user signups.

I'm optimistic of the web app user model after having developed desktop software for the past 10 years. Each version has to "work just like the previous, but better". You can only do that for so many versions :)