Well, prices tend to drop over time. One year after the release of World of Goo, it was available as a "pay whatever you want" package. In Sairas case, I wanted to experiment a bit with pricing. I didn't know exactly what price level that would work best, so I tried a higher level when I released the game (but I had the two licenses option for only an additional $2), and then when I released the game on Steam I wanted to try out how a different price would affect the sales. I know the downside is that some people may have to pay more for the game than others, but that's pretty much how it works with any products (I usually wait half a year after the release of an xbox 360 game to get it for a good price), and the stuff I learn out of adjusting the prices and checking the sales is really important.
Oh, and about the demo thing. I'm not sure why there didn't end up beign a demo of Saira on Steam. It's sure supported in the game, but perhaps it was me who was bad with communicating that to Steam, or perhaps I simply set up the steam package to them wrong.