From the FAQ:
Q. What does OEM stand for?
A. OEM (Original Equipment Manufacturer) software includes all essential components of Microsoft Retail products excluding support from Microsoft. Retail version comes in a fancy box, OEM does not. You will receive installation CDs only (no original retail packing). Although OEM software does not come with a box or a manual, it is the typical and actual software, no trial or demo versions.
Q. Am I purchasing some academic or trial software?
A. No, all software is fully functional and you'll get a FULL version of a product you ordered, not a trial one and will be able to use it indefinitely.
Looks okay to me. Who uses the manuals, anyway?