Dual pane windows come at a price point. They're heavier and more expensive so you won't see them in entry level Class A's, trailers or fifth wheels. Some people do the math and opt for an extra A/C unit vs the cost of dual pane upgrades.
For someone to say I wouldn't own dual pane windows because they saw so many posts about them going bad, is like saying I won't buy a car with power windows for fear they'll break. The percentage of dual pane windows going bad is probably less than half of 1%. Even then, it's usually one window out of 10-15 in an RV. :S
