This is so true.

We are a dev shop with a lot of experience with .NET. For our most recent web project we decided to take RoR for a spin. Things that would take an hour in .NET took us days. Not because RoR is lacking, but because we just don't have as deep a knowledge of Ruby or Rails.

Having used both, I can't think of a compelling technical reason to choose one over the other. I personally think .NET has a nicer tool chain, but RoR's tools are more than adequate.

Go with what your developers want to use.