I've been using it on some cheap ethernet-over-power adapters (Devolo, not "HomePlug" brand) for streaming MythTV recordings of HD UK TV for several years and it's been completely fine.
UK Freeview HD is 1080i though, but it's in a very bandwidth-inefficient container as it's just the transport stream which is sent over the network. I've also played some 1080p content over it with no problem, but most of the content I use is 1080i.
No idea how old my wiring is (house is from 1950), and this is across the distribution board / fuse box too, as it's between upstairs and downstairs in my house. So my experience is completely different to yours and much more positive :)
