I wouldn't say it was "silly" to have 1080p capable equip.
The cable companies broadcast HD in 1080i not 1080p (google the difference, takes too long to scribble down here...besides, it's been explained to death!)
Bluray is the only source material where you'll get 1080p. Is it worth it? Depends on the individual. If you're sitting 12 feet from a 42" TV then you won't see the benefit of the additional pixel count. If you're less than 8 feet you'll enjoy the step up in PQ.
The whole "1080p" thing is a great sales tool for retailers & manufacturers alike. It's a good bit of technology, but far from being the stand alone decision maker. You have to consider a whack of other criteria when making your choice...contrast/black levels, lifelike colour reproduction etc. I've seen many 720p panels kick the crap out of a lesser quality 1080p panel based on the other viewing factors!
You need a digital cable box to get the upper channels on the cable bandwidth. NOTE: a basic digital box DOES NOT give you HD channels!!
To get HD from the cable company you'll need an HD box (go figure!!!) same applies for satellite.
Once you have the aforementioned HD box, you can get the HD content to your TV one of 2 ways.
1) Connection through component cables (red, blue, green) A seperate audio connection is needed with this configuration...either analog L/R or a digital connection
2) HDMI cable. This will do the whole thing (however, some prefer to route the audio to a different input) I know here in Toronto, the Rogers cable boxes can have some issues with HDMI cables (get with the program Rogers!!)
You CANNOT get HD from your HD box with composite (single yellow RCA connector) connection, or S-Video either!!