Do you think it really make that big a difference?
I recently got a Sky+ HD box and came home today like "omg is that on the HD channel? It looks amazing!" and mum went "no it's not HD". And when I flicked through the HD channels they were no different to all the non-HD channels, in my opinion. And this was on a Flatscreen HD TV.
Maybe my eyes are bad but we're paying £10 extra for a few more colours possibly.