Considering the size of the prints, I'd say the pricing might not be totally off the chart. I'm sure the person behind the site has done the market research. Once you get into mural-size prints the target market is public display like corporate lobbys, a market with a completely different price sensitivity.
Also, with huge prints displayed so they can be studied closely, detail becomes more important and overall composition less important. So while an image might not work on the web, it can look fantastic as a 40x60". I've seen it with some of my own 8x10's, you have to go large to fully appreciate them, to get that immersive experience.