I think it's really absurd to say that a small amount of developers use it. It may be true but the only reason it's true is because so many XNA tutorials tell you to use the content pipeline which I think is absolutely absurd. Infact, I think the content pipeline is extremely poorly designed and clunky to use. I wrote my own resource system for my XNA MMORPG that works off of custom resource loading providers that give me a much higher range of use. Unfortunately when it came time to implement this for the sound provider I realized you could only load them from the content pipeline. There is really no reason that all resource types should not support the "FromFile" method. It's a single method and it opens up the possibilities to a much wider range.
And yes I am building my engine to work on the Xbox as well where I can simply write resource loading providers that use the content pipeline.
I bumped this thread because it's ludicrous that this isn't supported.