jrstubs :
I have read all the product descriptions but none are clear on this issue
None of them are clear at all. Even Microsoft has been incredibly evasive on this issue.
In general, OEM copies are supposed to be purchased and installed by a system builder who then sells the system to a third party and provides customer service for that system. The OEM licence belongs to the machine (not the user) and must be transferred with the machine when it changes ownership. In the past it was a violation of the licence to use an OEM licence for personal use. However, no one followed this and Microsoft changed the Windows 8 OEM licence structure to allow for personal use and for OEM licences to be transferred to a new machine. Retail editions of Windows are not bound to the machine on which they are sold with.
There is no functional difference between a retail copy of Windows and an OEM copy of the same edition. They are equally functional and will receive all updates and support from Microsoft.