I don’t think its a matter of making two levels of quality; its how optimized or tuned something is.
The NuTech DDW-081/-082 drive is a good example.
NuTech shipped the DDW-081 drive as DVD+R only. Then they released a beta firmware (marked with the DDW-082 model number) for the drive that supported DVD-R as well. A lot of people couldn’t get it to work reliably. Others had no problems with it.
Then NuTech released the DDW-082 drive which supported both DVD-R and DVD+R. Except that its the same drive as the DDW-081. So why can some write DVD-R fine, and others not well at all?
A NuTech employee said that NuTech would only support DVD-R on retail DDW-082 drives because drives that became marked as DDW-082 were hand-picked because they could handle DVD-R media without problems. Those that had problems were marked as DDW-081. People could use the beta firmware and if it worked for them, great. If not, oh well.
Seems very analgous to this situation. Sure, there are no physical hardware differences between the ND-2500A and the ND-2510A, but that doesn’t guarantee that all ND-2500A drives can write DL media without problems. Considering how little testing has been done and how few people have posted their experiences with DL media, it seems odd that anyone feels qualified to say “yup, they’ll all work fine.”
Oh, and I forgot to reference AMD.
With the Athlon 64 processors, AMD introduced a new process for putting 1 MB L2 cache on the processor. Except they had problems with the process and a lot of the chips had memory problems. So AMD disabled half the memory and marked it as a lower chip.
That’s why the 3000+ and 3200+ run at the same speeds, but just have different memory sizes. The 3000+ started off as the ones where the L2 cache had to be partially disabled.
Not quite the same thing there, but something relevant.