One might think so, if one is charitable toward the typical developer and they're abilities. I worked at a place that had implemented their own query language and integrated it into their core product.
The query language was interpreted, and walked structured text files stored on disk. Worked great for small installations, but as the company grew, acquiring larger clients, clients data corpi grew, performance fell of a cliff.
The syntax of the language was all over the board, users would cut and paste to combine little recipes to do things, there was a never ending stream of support calls as to why this didn't work like this, and why couldn't this do this like this other part does that.
Edit; wanted to say consistent, logical syntax is were someone with experience in language theory and implementation would have made an impact. The language as was, was the result of feature accretion. I think someone with knowledge would have attempted to craft a kernel of functionality, and back it with a more robust datastore (sql).
Edit2: also want to clarify, the developers who did the implementation were actually quite talented, the project was simply not something they were equipped to deal with, and really weren't given the oppurtunity to refine or iterate on.
Edit3: I offer this as an example of one company that implemented they're own langauge, of course the purpose of this example differs from wasabi, and is not intended to condemn or denigrate Wasabi, or Fogcreek.
I guess it was a net win, but it was painful.