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!
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.
Languages like ColdFusion and PHP are web languages that don't make much sense outside of the web.