Yes, it is still limited to two burners. But that limit applies only to two simultaneous
burners. And by "simultaneous" I mean both burners going at the same time burning the same bits to two separate discs.
Other than that you can use the full retail package with as many burners as you want, but only two at a time. For most people this isn't an issue, since they only burn one disc at a time anyway.
If you do want to burn more than two copies of the same disc at the same time, you will have to purchase the additional multi-burner add-ons. I think you can go as high as 32 burners at once.
By the way, as much as I have groused about the OEM serial-number policy, the upgrade to full retail isn't what I would consider truly big
bucks. It costs $19 to get a serial number over the web: