Enhancing any piece of software always requires a balancing act: what if the improvements also result in new problems for existing users? Over at APC, I've reported on what father-of-Linux Linus Torvalds had to say on the issue during a session at Linux.conf.au in Hobart. Linux is firmly built on the principle of not incorporating a fix, even for a well-recognised bug, if that fix in turn breaks something else:
The number of machines does not matter. you always hear about machines that break; you never hear about machines that work. If you tell me this fixes more than it breaks, I laugh in your face.
That's a rather different attitude to, say, Microsoft, which sometimes consciously makes decisions that stop older systems from working (such as ripping the original Windows help engine out of Vista, for instance), and frequently bases its design choices on the relative number of machines that will be affected. Photo from Wikimedia Commons