Why can't I mirror my ipad 2 on my Mac Mini running Mountain Lion without an Apple TV?

I was under the impression that with Mountain Lion that i would be able to use Mirroring, but i see that its only mirroring from Mac to Apple TV, or iphone / ipad to Apple TV. Why can't you use airplay to mirror my ipad to my Mac without having to buy Apple TV? If the new mac has airplay, why do i need Apple TV? My mini is connected to my 55 inch LED TV, thus i don't need an Apple TV to watch content. Seems redundant to have both really.