What is the difference between a 21" or 27" iPad, and a 21" or 27" TV that supports AirPlay from a regular iPad "with Netflix and HBO Go and iTunes Movies and T

What is the difference between a 21" or 27" iPad, and a 21" or 27" TV that supports AirPlay from a regular iPad "with Netflix and HBO Go and iTunes Movies and TV shows". OK, now make the "TV" a monitor, perhaps with an HDMI input for the cable box.