This is very true and also the reason that you can't just dump a bag of cash onto an OSS project and expect it to fare batter: Open Source projects run on time, not money. The only way to give it more time is to have more devs that are willing to commit their free time to it.
This is not to say you shouldn't give money to OSS projects. You should definitely support your favourite programs even if its just $5 a year for a single one you used that year.