No they aren't one and the same. As far as I'm aware keys for a retail disc are different from those for an OEM.
No, they aren't burned DVDs, they are original system discs which come in a box with a booklet and a licence sticker. I just don't know whether they're OEM or retail.
These discs are pre-SP1 which means that, following a reinstall, I would have to install SP-1 as well. Digital River is offering a system which allows Windows 7 to be installed with SP-1 incorporated which is much easier than installing from the original pre-SP1 discs.
I have an image of Windows 7 taken just after a reinstall from the purchased discs, with just Windows and security in place, but that's still pre-SP1 !