Why the constant upgrades?

If this question has already been answered elsewhere, just point me to it. Otherwise, why do I have to always be faced with upgrading my version on wordpress? I just get used to the features and the theme is one I like, and then I see that someone has created another version with even better/more/different features. And every time I log in from then on I see the suggestion to upgrade. But now it is not an automatic reload. Now I have to go through an outside source and I have to make sure that the theme I have actually retains the featured I liked when I set it up. I know that for the technically interested that developing new versions and plugins is an important part of their computing experience but for me, its like buying a new car every damn week when all I need to do is drive to work and back.

Actually, this might not be so unworkable if there was a way to see the upgrade in action before I tried it but this option doesn’t appear to be available unless I make up a test blog for myself. Anyway, I would really like to understand this all idea of upgrades for upgrades sake a lot better.