Memory Speed Question

Why does AMD mobo accept a slower RAM than intel ie DDR3 1333 vs 2200. Is it got something to do with the bus speed or the memory controller

Asus M4A77TD-PRO AMD accepts:
4 x DIMM, Max. 16 GB, DDR3 1800(O.C.)/1600(O.C.)/1333/1066 ECC,Non-ECC,Un-buffered Memory

Gigabyte GA-EP43T-UD3L Intel Mainboard
Support for DDR3 1600/1333/1066/800 MHz memory modules

From the examples you have listed, the AMD board supports faster memory? So I am not sure why you are asking about Intel supporting faster memory. At any rate, it means nothing, except that is what these particular boards are "capable" of running at the time of their release.
It means you can buy memory that is RATED to run at any of these speeds.
The OC setting mentioned means that there probably is no memory made at the time the board was released that you could buy at that rated speed. So to achieve it, you technically must overclock a slower module to get there, either by bus speed or multiplier.