There can be a difference. Not between Monster and moderately-priced cables, but between moderately-priced and cheapo cables. Anyone wanting to see the line in the sand for HDMI cable comparisons should read Gizmodo's scope comparison here.
FWIW, I run three Monoprice.com CL2-rated 35ft HDMI cables in my setup and despite what the Gizmodo article says, I have no problems whatsoever running 1080i and 1080p. I would absolutely buy them again.
I'm a little curious as to why the scope in the Gizmodo pictures shows what appears to be an analog sine wave rather than a digital square wave?
There was a guy on CL a month ago that had hundreds of high-end HDMI cables. He had a connection at Best Buy to buy all of the ones that had been "opened". I bought 4 8ft'ers and a 6 ft'er for $45. $5 or $10 each, depending on the length.
I checked CL, and he's in Crandall.
CHL holder and Conservative...AKA "Domestic Terrorist"