The change is that the IRS now holds the restaurant owner accountable for the taxes due on the tip. The result is that instead of the money going to the server directly, it first has to pass through the hands of the business owner. I don't know if this still goes on, but some years back I recall hearing that some restaurant owners would then "distribute" those tips to other members of the staff — the busboys, kitchen help, etc.
Traditionally, waiters always "tipped out" the busboys and bartenders they worked with, on any given shift, and better service (theoretically) promoted more generosity from the waiter. But now that the business owner has his hand in it, the business owner will operate according to his own interests. The waiter is cut out. The waiter has less control, and less direct incentive. The waiter has less of a payoff.
Rumor has it (or, if you will, common sense has it) that some owners abuse their role as middleman.