You are talking about this one right?
3M GTR Emblem 3D Logo Car Motor Decal Stickers - eBay (item 110661226438 end time Mar-18-11 19:56:01 PDT)

I'm guessing that some people just don't know where the design was taken from. Most people just want to make their car unique in some way and you don't see these everyday. (Well, at least they don't think so.... )
I do remember seeing some dealers at NMRA selling them a few years ago, along with other Mustang emblems. I am not sure if they still do, but that could confuse some....