On my TiVo, all networks went 720p from 1080i

So, I just noticed this... It used to be that most channels would be 720p, which is just OK, not great, but at least the local network affiliates (ABC. CBS, NBC, and even PBS) would be 1080i, which made their picture much sharper.  When did this change happen?

I understand Comcast wants to maximize their cable bandwidth, but come on people, can't you just keep a small handful of stations to a slightly higher standard?