Paypal, credit cards, etc. have dispute resolution services. They don't just allow the buyer to renege arbitrarily. To be useful, it seems to me that an escrow service needs to offer a more robust dispute resolution mechanism, which will cost money.
not sure what your point is, my point is that in a bitcoin economy you would have choice
for a large purchase either the merchant or the customer may insist on an expensive escrow service that deals with disputes robustly
for small purchases this might not be so important
I saw a comment on HN recently asking why startups never challenge the VISA/MasterCard hegemony, with a response saying it is simply to expensive to enter the market with a low ROI
widespread bitcoin use would lower the barriers for this kind thing, unless you like monopolies and cartels, I can't see how anybody would argue this is a bad thing (regardless of whether you think bitcoin is good, will suceed, whaterver)
in a large mainstream bitcoin economy there would be multiple escrow services, both the consumer and merchant can decide what services they will use
clearcoin has the option of donating the money to charity if there is a dispute, seems like an interesting innovation to me