People that are more price sensitive tip lower and every once in a while a waiter will experience an extremely generous tip. I'm not convinced that forbidding tips would increase net wages paid to servers.
In terms of who is paying, restaurants will simply raise prices to account for higher wages. Their margins aren't that big.
Finally I think tipping definitely incentivizes good service. Its partly cultural, but I've noticed much higher level of service in the US compared to Europe were tips are not expected as much