Things aren't quite so free-form as i believe you are imagining.
There are two specifications in particular that define how Memory is catagorized, detected, and configured: JEDEC Standards, and SPD Standards.
Basically, JEDEC defines the timings, cycle-time, clock-speed, etc of all ram that is sold as "DDR3-12800" (just for example), so that all vendors agree that the settings will be the same for all their chips in that line. See the specs for DDR3 RAM here: https://en.wikipedia.org/wiki/DDR3_SDRAM#JEDEC_standard_modules
Your motherboard implements Serial Presence Detect (SPD), so it expects the RAM it finds to be configured such that they conform to one of the JEDEC profiles for that type of RAM.
That means that when your Motherboard manufacturer says that they supports "Up to DDR3-2133", that (among other things) it's SPD is capable of recognizing DDR ram of all DDR3 types with a transfer rate of less than 2133, and has the ability to load JEDEC profiles to configure to use that RAM.
So, thanks to JEDEC and SPD, the motherboard manufacturer doesn't need to tell you explictly what profiles they support.