Conversely, you might be able to iterate faster with a 'web' language and create a product people really use in a shorter time frame and worry about scaling later!
5 years ago it might have been true that RoR was that much more productive it was worth using, but that doesn't match my experience today using RoR and Scala.
Update: To try to avoid turning this into a language war, there are other good reasons to use something like RoR. Ease of hiring is one. Using known tools is another, if you're not building anything you expect to get load.
