The reason tips apply for TS and not QS has to do not only with the type of work, but the base pay. There are different minimum wages in America depending on whether you get tips or not. A person working a job where tipping is expected earns roughly half, per hour, in base pay. The thought is they will more than make up for it in tips.
Also, keep in mind that for many establishments, the tip doesn’t JUST go to the waiter, but the tip is split among the main waiter and the helpers (those who help carry plates, who help clear the table, etc).
The reason it is based on the bill is because it, generally, then scales up appropriately based on the amount of work needed. While it is true that any individual meal choice varies in prices, it balances out. But a larger group orders more, and so the price goes up as does the tip. Also, if someone orders drinks and appetizers in addition to the main meal, the price goes up…but so does the amount of work. But it is also why in some places you’ll find the waiters will subtly push dessert or appetizers or drinks. They want you to spend more because they get a larger tip as a result.
Anyhow, for food, we always do 20%…and I actually do more, because I tip on the tax as well, which isn’t expected…and then round up to the next dollar. So, for example, if the bill were $30 here in Michigan, that would be $31,80. 20% would be $6.36, but then I then round that up to $7. (The reason I round up is because of an old concept I’m not sure applies any longer…but if you had poor service, but still felt you should tip, then you would leave the tip PLUS a penny. The penny was a way to indicate you weren’t completely happy with the service, despite the fact you are leaving a tip. So, to me, not having a nice round number might imply something you don’t intend to imply when the service was good!)
But tipping for waiters is easy. Been doing that my whole life. I just didn’t want to skimp on others I should be tipping but am too ignorant about. For example, I have never tipped housekeeping in any hotel I’ve stayed…but part of that is because when we stay in a hotel, it is generally a single night. In such a case, cleaning isn’t for me at all, but just part of the expectation of staying in a hotel. HOWEVER, staying multiple nights, the housekeeping service is not for your own benefit exclusively. So, I guess I can see tipping for that…although it never would occur to me to do so. Hence, the reason for this post!