I think this has something to do with the sense of ownership behind the software. An open source software is owned (literally and figuratively) by the people w

I think this has something to do with the sense of ownership behind the software. An open source software is owned (literally and figuratively) by the people writing it, hence they will take care of it as they take care of their own. On the other hand, propitary software is owned by some company (and its stockholders); it is written by employees payed to do so. The employees will come and go, only the company will remain; naturally this reduces the sense of ownership any programmer may have over the code and with it, the quality of the software. this is, of course, a very broad generalization riddled with exceptions and special cases. Not all software is alike.