If you want to pay the hidden costs for being beholden to Microsoft, fine, just don't complain when the pain starts e.g. the VB6 developers suffering because it was not practical to port some application. I saw this issue at work, with a legacy VB project.
As for community, Java has a far larger and more active community than .Net, and the .Net community even ports OSS platforms from Java OSS! If you look carefully, you can have a totally free development environment in Java, with very little lock-in, forget that with .Net, BTW an don't regard Mono as serious competition given it's lack of (probably patented) libraries.
Well this Java developer see no good reason to move to a less flexible environment, like .Net, with less libraries (even with some ports from Java) and less capable support products. I have so much OSS choice (e.g. Castor, Apache XML, Apache Jakarta) that we don't need to buy any software components, this really does save money and time! I once needed to load and process massive XML files, Java did fine, all the Microsoft 'solutions' failed!
Sorry to break your bubble, but many people do not trust Windows for mission critical systems or do not want to change over to Windows compatible systems (very costly for a large estate), in these instances you need portable software, Java makes this easy and we have used this flexibility.
Lastly, I have a pared-down Windows system (heavily secured and non-microsoft firewall) so that I can use some Windows only software and hardware, but I would never use Windows for a mission critical server given all the performance hits, security hits and system maintenance issues, the TCO is just too high. I have no problem putting software on a customers Windows server if that is what they use, I naturally assume that they don't mind the extra work and downtime. We have even had customers compain about Windows bugs (not our software), but politely told to get lost by Microsoft.
Have a look at this rant, in amongst the angst and wordiness, there are some quite valid reasons to avoid all Microsoft products e.g.
http://www.vanwensveen.nl/rants/microsoft/IhateMS.html