No, you are right about that...see here's the thing: The $20 cables cost about $4 at cost. The $50 cables cost about $5 at cost, $75 cables at $6, $100 cables $10 and so on. Really it doesnt cost any more for monster cable to add 3 layers of cable inside the shielding than it does for them to do the single layer of cheap cable. It's almost the same amount of material involved in either a $20 cable or $100 cable. With the large factories making huge amounts of cable, the difference in cost to manufactor a cable in a particular way is nearly nothing.
They use the same wiring for all the cables, the only difference in cost is just the nicer connectors and thicker shielding.
Most of the cost you pay for is branding costs, which in Monster's case they have a huge reputation with the less than knowledgable and they will fight to the death to keep their name, and so far they have won almost always (I think monster.com is the only place that has thwarted their lawsuits.)