there does seem to be SOME benefit to a high quality digital cable. I totally used to believe in the on/off theory, either it worked 100% or 0%. but it does seem as though there's some error correction that allows for a few missing bits here or there, and with longer lengths I have noticed not so much a change in picture quality, but in reliability. some cables have a host of handshake issues, or drop connections occasionally, while others don't. in either case, I do have some 'cheaper' cables that work sometimes, and sometimes not so much, and other times not at all. it seems to be affective by the content being played. ie, the desktop of my computer, totally fine. but playing an HD video, won't work at all. something in the middle like viewing webpages, or video that's not fullscreen will kind of work, but drops the connection frequently.
now that all being said, I'm not saying a 75dollar cable is necessary. more that a $6-$10 cable from monoprice is worth buying instead of a $2-$3 cable from china.