I think you are exactly right. STA owners aside, I suspect there are not many ST owners looking at big brake kits and performance parts. For those that do, an exhaust and CAI kit are sufficient so that is what we see in the market.
STAs are not yet plentiful enough to have piqued the aftermarket's attention. Again I haven't followed Ford performance very closely and incorrectly assumed when I bought this that since it was a 4.6L I could "do anything you could do to a Mustang". The truck does does stand on its own merits, it would just be nice to have a few more performance bits to choose from. I would be interested in better brakes if anyone is familiar with a BBK setup.