The available write speeds are in the drive itself, and are not controlled by the software. The drive has a list of media, by MID, and had write strategies for each individual MID it knows.
I am sure ProdiscF02 is in the firmware, so it is probably likely that Samsung [TSST] has limited the write speed to 4x for quality reasons. Other 16x media is also limited to lower speeds, such as SONYD21 [Sony’s 16x DVD+R] being limited to 6x, etc.
Roxio queries the drive, asking “What Speeds Should I Offer?”, and the drive responds “I know ProdiscF02 as a disc able to be written at 2x and 4x, so that’s what you should show.” At least, that’s how I imagine it.