Impedance has a significant effect on high frequencies, especially in longer cable runs. It's not as simple as "it either works or doesn't". If the impedance of the cable itself is significant enough, you will have problems with a digital signal. That's why on longer runs, you use higher quality cable.
Monster is not higher quality cable. Monster is higher quality marketing.
There are only two factors that are really important about cables in audio: impedance per foot and capacitance per foot. What's tolerable depends on the length of the run.
+1.
Speaker wire is just two big conductors of a higher-power, low-bandwidth signal. HDMI is very high bandwidth and it subjects itself to cable quality due to attenuation. It's more noticeable on long runs, of course.
That's not to say a Monster cable is every required - there is ZERO reason to purchase expensive cables like that. But a
quality inexpensive cable may be required, a prime example is longer runs.
Connectors and wall plates are also an area where cheap product can subject high-bandwidth signals to sufficient problems, as well as shielding.
How does a higher quality HDMI make a difference? With a digital signal, it either works or doesn't. Theres no difference between the $35 walmart cable or the $90 monster cable.
Wrong. Ever own a satellite when it's raining? With sufficient interference, you get signal breakup and the picture gets lossy. Same with HDMI - they call it "snow".
The higher the bandwidth, the more cable quality/construction matters.