Not all of them ... with both MonoTouch and Unity you need to have a Mac OS X running with XCode installed, otherwise you can't sign, package or test your application in the IPhone emulator.
If this announcement is about developing, packaging and testing iPhone/IPad apps with only a Windows workstation within Visual Studio, then that's certainly good news.
Not to mention that MonoTouch and Unity are legally both in a gray area right now ... because they are explicitly disallowed in the new SDK EULA and Apple hasn't mentioned their official position on them (AFAIK).
I want to clarify the legal issue, though. There is no (non-patent) contest on MonoTouch or Unity's right to existence; people are free to make iPhone runtimes, compilers, etc., as much as they want; the issue arises when developers deploy these techs, as Apple's new EULA is applicable only to developers. While the effect may be the same (no use), I think it's an important distinction.
If this announcement is about developing, packaging and testing iPhone/IPad apps with only a Windows workstation within Visual Studio, then that's certainly good news.
Not to mention that MonoTouch and Unity are legally both in a gray area right now ... because they are explicitly disallowed in the new SDK EULA and Apple hasn't mentioned their official position on them (AFAIK).