California -
http://www.dir.ca.gov/dlse/faq_tipsandgratutities.htm
Note the words "over and above" i.e. it's
extra, not actually part of the wage.
(Same link).
Voluntary. I.e. if you don't pay it you aren't a thief.
You are misreading your own source.
"Gratuity" is defined in the Labor Code as a tip, gratuity, or money that has been paid or given to or left for an employee by a patron of a business
over and above the actual amount due for services rendered or for goods, food, drink, articles sold or served to patrons.
Further down, if you had read #6:
...An example of a mandatory service charge that is a contractual agreement would be a 10 or 15 percent charge added to the cost of a banquet...
When the menu says a 18% gratuity will be added, it is a service charge. It is part of the bill when you have x amount of people (seems to vary by establishment of over six or eight or more).
And to support my position even further, here a snippet dealing with Pennsylvania (where this actually happened):
"One last possibility involves the practice of charging a "gratuity" or "service charge" collected in lieu of tips. In that case, the money is not even viewed as "tip" for minimum wage law purposes. As a result, no use of the tip credit is allowed and, as you might expect from the above discussion, the gratuity money can be divided up however the restaurant owner desires. The restaurant owner can cut in or out classes of employees as he sees fits -- provided that his decisions do not amount to discrimination under Federal and State anti-discrimination laws, which is a topic unto itself."
http://www.buteralaw.com/newsletters.asp?c=88&id=597
Other readings indicate a gratuity charge on a bill in florida are part of the bill and not just 'helpful advice'.
Buyer beware.