Actually we have also an Intro Campaign, Buy Professional now and Get Free Upgrade to Enterprise in Jan 2012 when released. You have to buy it before Dec. 30 though

No we do not license per year (except for Grid++ Services), you get a license for the major version of XPower, thus until the next major release fixes and updates are also free, and each major version is supported and fixed for 3 years, so in 2013 when XPower++ 3 comes out and you are happy with 2 you can stay on version 2 for at least three years.
But generally our pricing policy is very fair, so upgrade price to version 3 will not be very high

I hope you will like our product and buy it.

Please also have a look at our roadmap on our site (at the bottom)