reven: they need to try and work on getting mepo on different clients/hardware.
I think this is one of MP's weaknesses (and XBMC's strengths). However, compare the size and makeup of the two development teams and you'll start to understand why MP is Windows only. Also MP's top feature is native TV support. Until the last few years almost zero TV cards had Linux drivers, so what was the point of having Linux support (?). This is changing with companies like TBS, TeVii et. al. bring Linux drivers to market for well priced and featured hardware (and chip makers investing effort into producing solid reference drivers).
Having said that, there are projects like MpExtended and aMPdroid that are bridging the gap to other platforms.
this is hard being in c#, but they have moved most logic into a client/server setup (more so with mepo 2 i believe, centralized database.), so they could write a gui that runs on more hardware (linux, android, windows etc) then they might get more users.
As you know, XBMC is able to achieve platform independence by using platform independent technologies such as OpenGL and C++. There are core parts of MP that are C++. MP is tied to Windows as much or more by the TV support framework (BDA) and DirectShow as C#.