NO, they do not need to subscribe to cable, just acquire a simple converter box which will convert the HD signal to a form that works on their older model t.v., or if they have a television that is newer and already HDTV enabled, the signal change will not affect that unit at all.
Also, I do NOT believe someone in a rural area without cable has Caylee. What I believe is pretty much irrelevant to this case. Either Casey or someone else will be charged based on actual facts and EVIDENCE, or Caylee will be located based on the same. Unfounded speculation and name calling will not contribute to the outcome either way.