I agree that service is generally better in North America (vs the UK, at least), but I'm not convinced that the tipping culture has much of an impact. Tipping is so customary in the US that I find most people just tip the same amount - give or take 5% - even if the service was terrible.
That's extremely anecdotal, and I have experience in the other direction. I don't tip if service is terrible, I give over if it's great. I don't have numbers, but I'd assume people who have awful service will more likely tip less or none.
