Things that make you go "Huh?"

We recently went out to eat and were surprised looking at the receipt...

... we've become accustomed to suggested tip amounts being shown on the receipt, but usually 15%, 18%, 20% -- this one was 20%, 25%, and 30%!

We were discussing how it used to be that the tip was 10%, and it was for the service rendered, and wasn't "expected" but designated that you appreciated outstanding service. Even though the price of restaurant food has increased (and so 10% of the total would have been more money to the server), the tip is now "expected" and at 15% or above -- we're not sure why the percentage expected rose. We typically tip at the 20% level or so, but we generally tip on the total of what we purchased, not tipping on the tax (so, in this case, we would have tipped on $34, not $36.38 -- a nice feature of this receipt is that it explicitly indicates that the suggested tip amounts are on the total check price -- even though we wouldn't use their suggestion, it is nice that they state how they calculated it).

I think the argument is that since service workers are paid less than the minimum wage for other workers, they need tips to make up the difference. Why are service workers paid less? 

Are folks who work in beauty salons also paid at the lower rate?

What about massage therapists in a doctor's office? I tip the massage therapist, I would never tip the doctor...

I should probably do research to understand this more!