I have worked on plenty of successful fixed price software projects. The simple reality is when you fix costs quality becomes the flexible metric, but meeting the minimum project goals becomes really important. However, considering how many software projects fail, reaching the agreed upon minimum at the agreed upon price is vastly better than what generally happens.

As to failing to finish a project the wonders of fixed price contracting is you can pay at completion of some milestone. Of course that means people need to pad the price even more ahead of time to assume that risk, but price becomes a really useful signal.