Upon further reflection, I'd say that for the company in question, for that particular sector, having the query language available was a positive differentiator in the marketplace. I think it's clear Fogcreek's use of wasasbi was necissitated by the business and tech climate of the time. So clearly there are compellings reasons to go down this path.

I'd also say that languages are hard, runtimes are hard, languages and runtimes together are really hard. A decision to go down this path should be carefully considered, and not because a developer on staff read Parr's Antlr book and wants to try it out.