Tubes (but not for the internets...)

I am seeing more and more PEX plumbing in houses that I visit. From what I understand copper is getting more expensive and this is driving the market for PEX. This of course confuses me as I have read that many plumbers charge the same price. The difference is that most PEX installations are run from a manifold in the basement and each faucet has its own individual run back to this manifold. With this style of plumbing you don't have to worry about the flushing the toilet and getting scalded in the shower. But for my money I would expect for a plumber to design a new house correctly and even with a traditional plumbing design this should not happen. So my theory is that plumbers are just making a lot more margin on PEX.
I also wonder about the health effects of plastics. Water is the best solvent around and I just have a hard time believing that there is no off gassing. I found one good article about a specific type of PEX that is bad. So when I finally get around to building I will consider PEX but only if it significantly cheaper.