I guess the cloudy ones that really stand out are the Neons, must be because they are positioned towards the sky more than other cars. Rick
You must not be looking very hard. I see Toyota with yellow lens all the time. SO's old Camry was terrible. I have a '92 F150 with some really nasty looking headlights, but my other recent Fords seem to have held up just fine. And even my '86 Sable had good looking headlight lens after 10 years (traded it then), but the stupid light bar looked pretty bad. I have a friend with an older Buick LeSabre ('91 I think) and it has some pretty nasty looking lens as well.
I suspect some vehicles suffer more than others because of where and how they are driven (because the outer coating is abraded off by grit). For instance my F150 has spent a lot of time on dirt roads and dusty fields. I assume that all this exposure to dust must have eroded the lens' surface - I know the bumper looks like it was sand blasted in some areas (painted steel bumper).
Ed