Who says there's no free lunch?
We say have your cake and eat it too. There are an incredible number of brilliant dedicated people with serious skills who are diligently building the information infrastructure of the people. These awesome (and shockingly altruistic) resources should be neither ignored nor underestimated.
Why reinvent the wheel? It's a rhetorical question. If it's already been done right, we don't do it again, we just pick up where our comrades have left off and make whatever customizations are necessary to meet your requirements (so you'll get exactly the wheel you need; no more and no less).
It's all about open source. It's not just the best practice, it's a way of life. We open source every custom solution we can reasonably generalize, and contribute to existing open source projects wherever we can make an improvement. We think of it as kicking what we've got into the global booty. And we leverage that commonwealth at every turn. It would be straight insane to do it any other way.