Well 8x media are often cheaper then 16x media. The vast majority of burners burn even 16x media with better quality at 8x (or perhaps 12x) then 16x. The time difference is not really that great so unless your some sort of DVD mass producer, it's not really that great an issue for many people. Also, in a number of cases, especially if you continue using your computer while burning, 16x might be a little too fast so it may just be frequently stopping and starting. Even if you use a resonably sized, e.g. 128mb secondary buffer this is not uncommon. It would be better to just burn at a speed that rarely stops and starts rather then one which continually stops and starts.
More importantly, the question is if we don't buy a 16x burner what are we going to buy? Slower speed burners are rarely available and even if they are, they are frequently not cheaper. More importantly, a 8x burner with most new media (or even old media) would be worse then a 16x burner!
Of course if you are talking about upgrading then it is a slightly different issue. Still burn quality is an important issue for many and if your burner is starting to die for whatever reason, clearly it's not really an upgrade. While there are undoutedly people who buy a new burner even 6 months - 1 year as a hobby, I think the vast majority are either buying a new burner (first time) or are upgrading their old burner because it's not working very well (whether because of firmware issues with new media or because it's too old). Note that 100 or so people is not a lot of people