While explaining why he blogs, Dave Winer explains something interesting about product development:
When I started blogging it was mostly to get a bunch of stuff off my plate, ideas I couldn't do anything with, things I wanted even if I couldn't create them. I hoped other people would read this stuff and someone would create what I wanted, and therefore increase happiness. Over the years I learned that this very rarely happens. People really want to come up with the ideas, even more than they want to be successful.
This sort of thing is very noticeable in open source projects - the developers will work on what interests them, regardless of what kinds of polish might be required to "finish" the product. This befalls commercial products as well; it's quite common to run across areas of a product that fall victim to the "80% rule" - 80% (the interesting aspects) of some feature get built, while the remaining 20% of "spit and polish" never happen - because it's considered uninteresting by the developers.
I've come to the conclusion that only a real user base motivates people to "finish" products. And even with a real user base, the less income that is tied to the work, the less likely it is to ever get done...