Indie games made for xbox live arcade are made through C# and XNA. Otherwise if you are an official game developer company, you could probably code your games from scratch and get them to run on the xbox. There are several reasons why RMXP games won't run on the xbox. First of all, all data files are saved using Ruby's serialization. The xbox has no way of reading these files without the help of IronRuby but IronRuby runs on .NET where the xbox doesn't.
However this french developer is working on an engine called GEEX that takes an rmxp project and converts it into an actual XNA game and allows support for the xbox. However to get it onto the xbox would actually require a license which is I think 50-100 dollars a year.