There's a bit of propoganda sure, but local people on local climbs have melted carbon rims from many other brands and when product X Y and Z are all known not to melt then that trust is worth a whole lot of money to some people who value their lives more than their dollars. The chinese or taiwanese no name wheels might be just as good or better, but "might" is a scary word if you're riding 50mph on a 14lb piece of plastic.
The melting issue is less of a big deal than you think. Just yesterday I completely failed to convince a triathlete acquaintance not to buy a carbon clincher wheelset. My arguments were dismissed along the lines of "well, clinchers might melt, but tubulars can roll off if you don't glue them properly and it takes too long to fix tubular flats". I was told that clinchers dominate in triathlons. The person is going to spend somewhere around $1500 on a pair of brand-name carbon clinchers and melting concerns do not even enter.
Nor is it about know-how and reverse engineering. Zipp has no trouble selling carbon tubulars and charging 5x the price of a Chinese equivalent. Tubular rims are extremely simple in construction and I don't think there's much know-how involved (magic dimpling notwithstanding). If the competitor can get the formula for the brake track ceramics, they have everything.
I think it's just that the target demographic is relatively wealthy, can afford to pay extra for some vague notion of confidence, and isn't able to enunciate the object of their confidence. Why is it that big brands can get away with charging $3500 for a carbon road bike with 11-speed Ultegra group (Trek Madone 5.2), when you can get a functionally identical bike at bikesdirect for $1400 (Motobecane Sprint CF)? Because the buyer pays $1400 for the bike and $2100 for the trust that the frame will not snap at the first pothole, that the drivetrain will be functioning properly, etc. The buyer knows next to nothing about carbon fiber except that it's light and it sometimes snaps. He does not understand what might cause the frame to snap, never saw a broken frame in person, has no friends with Motobecanes, to him it's just a black box that either will fail or won't fail, and the best rationale he can offer for paying $2100 extra for Trek Madone 5.2 is something along the lines of "but surely Trek has better quality control".
A competitor can step in and produce wheels which are identical to Zipps in every way but at a fraction of cost. But, if this competitor can't generate the same level of confidence as big brands, it can only sell them at the same price point as noname Chinese wheels. And if it can generate the same level of confidence, it has no reason to sell them much cheaper than Zipps.