The other issue is reliability. If someone goes to the trouble of creating fake flash drives I do not see them using the better quality components within, including whatever flash memory IC they choose to use. I would not be at all surprised to see production line rejects (scrap) used for the flash memory. Such QC fails are not something I would want to trust my data with. Using junk flash memory is more trouble than it is worth in my opinion. If a USB stick turned out to be a fake I would chuck it in the bin without hesitation. Having such knocking around my workspace is just asking for data loss so why bother risking it ? A flash memory IC may pass a single, or even multi run test, but that does not mean it will not suffer from flipped bits over time.
I had to laugh about this. Flash is made in several grades, based on the density. Some years ago, they started making flash with more than one bit per cell. That means multiple levels of voltage have to be detected. So there is a very clear tradeoff between cost and density. The highest density had 16 levels or 4 bits per cell, the last time I checked. Pretty much all consumer flash that isn't sold specifically as high quality (and high dollar) flash, most likely uses this high density, low cost devices. You will be lucky if it doesn't fail in the first couple of years.
So, no, these fake devices certainly don't use higher quality flash chips, and in fact, may well use factory seconds, etc.
I have some junk SD flash sticks with my company logo on them. Seems it is so cheap to laser etch the metal wrap, that they will do it for free, even on the fake flash.