At least in the Baltimore area, according to some of my students at the university and my niece, this particular set of laws are just not enforced as they should be or there are enough loopholes to allow employers to get around them... But thanks for the link I'll pass it along to them.
Now that being said, yes if service is lousy there will be no tip or a lousy tip, if service is great I tip more. I tipped our waitress at outback about 25% last night just because she was absolutely fabulous, on top of everything never had to ask for more bread/drinks she was there with it right away. Way more than I expect at that outback so gave a good tip for good service.
The 18% and 20% are suggestions, a lot of chain restaurants are now printing the 15% and 20% tipping amounts as a courtesy for the math impaired . You can tip whatever you feel is proper, or not, most CM's will not chase you out the door, if they do take it up to the manager and guest services as that is definitely very un Disney and I cannot see management allowing that kind of behavior from a CM.