As per reinventing the wheel . . . Linux . . . Open Office . . . GNU . . . Perl . . . UNIX . . .

Each of those things were created because existing wheels were simply not round enough in one way or another. Linux was created because Tannenbaum wanted to spend his time as a professor, not as king of the hackers (as he himself put it in a recent essay). Open Office was simply an Open Source version of StarOffice, built out of a need for an office suite not made by Microsoft. GNU reinvented all kinds of wheels for mostly political reasons. Perl and Unix were created because of the ineffectiveness of existing tools.

In my mind, there are two reasons for reinventing wheels, as the examples above show: 1) existing wheels are not good enough (either for technical or political reasons), or 2) you want to learn how to do it on your own.

#2 is usually not relevent in a business environment, because its hard to justify to your boss that you should spend a lot of time coming up with a solution that someone else has already solved and is freely giving away. OTOH, it might be done during off-moments at work or other spare time. #1 will be the more likely case.