http://bugs.winehq.org/show_bug.cgi?id=23816
--- Comment #12 from Vincent Povirk madewokherd@gmail.com 2010-07-29 12:47:21 --- MS .NET Framework is a second-class citizen, and it should be treated as such, just like all other Windows components that can be used in Wine.
Mono is an upstream project of Wine that provides (among other things, most of which we're not using yet) a CLI interpreter and class libraries. Mono cannot be used in place of .NET on Windows, and so running Mono on Windows cannot tell us whether a particular bug is in Mono or Wine. Since there's no easy test, Mono-related bugs have to go SOMEWHERE to be triaged, and the place that makes the most sense is here.
Since Mono does not and should not act as a .NET replacement on Windows, it needs help from Wine to do this, including replacements for the interfaces used by Windows programs to interact with .NET (such as mscoree.dll).
It should really be there by default, like Gecko, but I've not yet been able to do a complete Windows build of Mono on Linux, so for now we have to rely on the official packages.
if Mono is not installed, programs should ideally see that .NET is missing and try to install it, but it's more important that programs see .NET as installed when Mono is installed. Since most installers use the registry or filesystem to detect .NET, I can't have it both ways. If this ever causes a problem for .NET installers (which, to my knowledge, it hasn't), programs like winetricks should be able to work around it.