I'm going to guess that 'older' systems can't use AirPlay Mirroring because the display cards in those systems don't support HDMI over Wifi, which is basically what AirPlay Mirroring actually is. And that WOULD be a hardware issue.
So, DanAnderson, found this for you Mountain Lion AirPlay mirroring v. AirParrot: fight! | Ars Technica It states that how apple integrated airplay mirroring by using technology that is ONLY in intel's sandy and ivy bridge integrated grahpics chips. It is a good read.
And please remember to use tact, Kappy is one of the most helpful veteran members of this forum and should you need advice one day you may want his help. I know that Kappy would be a big enough person to help you even if you acted like a tactless jerk.