Ask HN: Is the OS stack a factor when developing deployable apps?

For my next project I plan to develop a web service that is aimed soley at the enterprise.

While I'll also offer a SaaS option, I think most companies will prefer to install on their own servers. I was wondering for this scenario, if I should stick with .net/Java or installing configuring PHP/Ruby/Python is an OK requirement.

I'm well familiar with ASP.net and RoR but was leaning on RoR for this project (as my day job is .net and wanted a change) but I have that nagging voice in the back of my head saying most companies won't bother installing/configuring RoR to use my product. Any experiences?