As much as i dislike the constant updates myself, this is inevitable with any system, software. Hackers are hacking, and wordpress needs to respond with better security and features. WordPress has made it very easy to upgrade to the newest version, if only you could upgrade your WINDOWS Version the same way the world would be a better place.
As far as the default theme being overwritten for OP, like previous posters suggested just rename the default theme to something else and you should be fine,, without having to update your theme every time, (wow what a hassle that must have been, i hear ya), i wish you have asked sooner.