I doubt that it is Spike that is overly compressing it. It is more likely that Direct TV is overly compressing it. Cable and satellite service providers do such things to save bandwidth, as a cable or satellite is capable of a finite amount of data transmission, and they can fit more channels on if they compress the hell out of it all. They typically sell you the service based on the number of channels, not by how much bandwidth each channel gets. If you use an antenna, you are less likely to have such problems, though, of course, Spike TV is, I think, not broadcast normally.
This, by the way, is one of those cases that really proves that "you get what you pay for" is a lie. Free broadcast HDTV is typically less compressed. See:
http://www.audioholics.com/tweaks/connecting-your-system/get-high-definition-hdtv
It is really pathetic, though, if a "HD" channel looks worse than a DVD. Are you sure it is really an HD channel? If so, you are getting screwed royally, as you are paying for HD channels that don't look as good as SD can look.