Licensing is not the same thing as validation or the technically possible
Technically the guy is right about OEM copies, but there's an interesting loophole. Remember the definitions (see below) of oem/upgrade/full products and ponder the following scenario :
What is interesting is the list of qualifying upgrade products. I can't immediately find this - it appears to be an earlier release of Windows. However, if OEM copies are included technically it is permissible - even under the EULA rules to :
1) in place upgrade the OEM version to Windows 7. This destroys your OEM license forever.
2) Congratulations - you now have a full retail version of Windows 7 on your old system.
3) Deactivate on old system. Transfer to new system.
The disadvantage of this is that you now have an old unlicensed and unusable system, but seeing as some people are trying to transfer OEM licenses that would be the end result anyway.
Different versions :
Upgrade : May require a qualifying piece of software. Once upgraded you can't use the old piece of software and the licensing terms remain the same as the full product.
Retail (full) product : Looks like it can be transferred serially to any number of computers you wish, provided it is deactivated on each old one. Can be sold to one other person, who cannot then sell it on.
OEM : tied to the motherboard. Can never be transferred. Should, to follow the letter of the license, be installed using the OEM preinstallation kit (yes, I know few people actually do). The fact it may ask you to reactivate if several hardware components are replaced does not modify the fact it's still tied to the motherboard. The motherboard must be replaced with an identical one if it fails, or at most one of comparable functionality - it is not a loophole to buy something new and fancy. Microsoft will need to re-enable such a new motherboard by phone, and they are known to refuse people selecting a dissimilar motherboard.
Also, the OEM copies do not need to be sold with hardware. They can be sold to anyone and installed on anything. The *only* differences are being tied to a motherboard and having no support calls from Microsoft.
You can argue about whether the conditions are legal or what you think is right but those are the conditions. Be pragmatic - do you want to be legal? Then buy the appropriate version. If you just want cheap software and rankle at the pricing then pirate the software - paying money for something you know may not be legit anyway is a bit bloody stupid.
Besides, Windows 7's pricing is currently such that Home Premium is pretty reasonable especially compared to older versions. If you want it, buy it now.