Sony has also had a very liberal policy for upgrading their video editing software.  I purchased Sony Vegas Pro and skipped several versions but I still have the option of getting the new version at the upgrade price.  If an upgrade only comes out once every few years (like Poser) it's not so bad, but when a company upgrades it's software every year it becomes costly and difficult to keep up.  I have found that I've just learned or gotten a 3rd party book about the newest version when they release the next version.