Why am I forced to buy SD movies from my computer when I can buy and download HD movies from my AppleTV?

I have been buying HD Movies with my AppleTV2. I prefer to buy the HD version. I have well over 300 as of this time. The process goes, to purchase the movie on iTunes with AppleTV... then download the HD and SD versions, plus iTunes extra to my Mac's (external) hard drive for playback thru my AppleTV to my large flat panel TV (in HD). I do the exact same thing when I purchase a (Pre order) movie from iTunes. Everything works well and everybody is happy. The thing that I can't understand is that when I brows the HD movies in iTunes and go to purchase the HD movie, an error pops up telling me "this computer can't play back HD movies". It then "forces" me to purchase the SD version for a lower price. (Computer is MacMini - but I have others that do the exact same thing) This bug has happened to me using iTines for a long time. Shure, I can power up my TV system... but I should not have to do that. I am shure there are other users that have had or are having this "problem" Sometimes I forget to order the movie when I do power up my TV system. I would appreciate any soluton to my problem if you have one.

Thanking you in advance

Alex Taylor