I wouldn't call it magic. I guess that after that a solid base is implemented. Maybe they will have some reusable components and not to forgot they will have learned a lot during last days / weeks. So they don't have to struggle around with minor issues that just consume time without producing an incredible outcome ... I'm also a software developer and know the issue of solving "problems" the first time. In the future you will smile about such issues and implement them in 5 minutes where you need maybe 1h few weeks ago...

Also i could imagine that it is a time intensive task to implement an exchange cause of the security constraints, backups, reliability and all this other shit around. If you solved all this problems once, you know how to do it in the future ...

Of course these are just my assumptions. I'm not a part of the PXC-Dev team so i don't have any deeper insight then you