Even so, that usually applies only up to a certain point in time. Once the company is big enough, they'll hire an army of maintenance programmers to continue improving the software.

For example, Tom Proulx wrote the first version of Quicken basically singlehandedly, but it's probably a whole department inside Intuit working on it now. Paul Buchheit is normally associated with GMail, but the GMail team is huge. Linus Torvalds wrote the first version of Linux, but hundreds if not thousands of people have contributed patches.