I think it is the manufacturer's responsibility to add support for different media types in their drive. Just because a drive recognizes a media code doesn't mean that it's something that Pioneer sanctions or recommends. And they don't have to do a spectacular job of testing fine-tuning the support for that media type. But to leave support out entirely is negligent, especially considering how easy it ridiculously would be for them to just add an entry for a new media code to the firmware's table and copy-n-paste in a TY write strategy (which would have the exact same result as disc makers using fake codes, except they won't need the fake codes).
It has been stated by a number of people from the Asian region who are somewhat familiar with some of the politics there that the Japanese companies are not very keen on supporting the various lower-tier non-Japanese companies while the Taiwanese companies are much quicker to do so, hinting at corporate politics. Don't know how accurate this is, but I've seen it be stated at CDF and other places. Probably the highest profile case is Optodisc using a fake TY code because, while they were able to get all the Taiwanese companies to add support, the Japanese companies wouldn't, so for some time, they resorted to using fake codes until support was finally added and they reverted back to their own code.
So yea, I think it is the manufacturer's responsibility, especially if doing a sloppy job requires so very little effort and is still better than doing nothing (if anything, to reduce incentives for making fake media codes).