Current speeds are not really enough for HD video. Even if you get 1080p video online it is still highly compressed for online transmission. If I remember correctly I think blue ray is 40-60 Mbps. Higher compression means there simply isn't as much detail.
Over the air HD in 1080i format is generally about 20Mbps. It looks pretty darn good to most people.
Yes, higher bitrate makes better pictures, but for TV, over the air is currently the best way to get network programming in the least compressed format.
