The answer to this question is that there is no answer. You see--it's kind of like the good ole' "AMD versus Intel debates" in that you can make an argument for or against Monster products. True, retails stores make lots of $$ when they sell Monster products. I actually can get Monster stuff for 60% off retail.
I have never attended, but talking to some of my fellow associates, Monster does large training/demo events for retail sales people--they do everything from disecting Monster Cable and comparing it to standard cables to playing back "an identical song" using "identical equipment" and just changing the cables. All the associates I've talked to say that there was a difference in sound (but note that they did their listening test AFTER they did their science experiments on the cables).
I use Monster products just because they could, possibly, improve the sound quality from my PM 5.1s (I am going to Monster my PM 4.1s this summer)... since I can get them for an affordable price, it's worth it. BUT... I honestly can't hear a difference either way... if I had to pay full retail price for the cables, I would probably look elsewhere.