Oh, man that statement makes me cringe. Have you ever replaced a piece of proprietary technology with a different one before? I promise you, you will consider this decision up front much more closely next time.
Yes, this sucks, as anyone who's gone through a rewrite can tell you. But the broader perspective is that this is what software engineers are paid for. If you could just build a system and let it grow with minimal tweaks, the only people the software industry would employ would be technical founders.
[1] http://static.googleusercontent.com/media/research.google.co...
In my experience, you often iterate towards a replacement instead of pulling the rug out from the current platform and replacing it with another. This isn't always true, but in the case of CRUD based web apps, it's a lot smoother in my experience.