No, Sfar, it is NOT required to use a 20A receptacle on a branch circuit rated at 20A UNLESS the receptacle is the ONLY one on the circuit. Why don't you test this in your own house: Kitchens required 2 20A circuits (GFCI-protected), and bathrooms require a 20A circuit (GFCI-protected). Go down and look at your electrical panel. If your wiring is reasonably recent, you will see 20A breakers for both and 12ga wire coming out. Now look at the outlets themselves. I'm willing to bet that at least some are 15A GFCI (or GFCI-protected by breaker or upstream GFCI outlet).
And to my buddy Steve, it's been a while. We'll catch up soon.
I hope that clarifies things, Kenbo.
Michael