Yes, there are OEM and Retail versions of some (not all) motherboards and memory modules. From my experience, the difference boils down to packaging, accessories (none - limited with OEM versions) and the manufacturer's warranty (which usually comes only with the Retail version). I don't believe there is any difference in quality or performance!
BTW, the above also applies to OEM vs Retail CPU's and HDD's (the exception being that some OEM HDDs do come with a mfr warranty).