Exactly. And for games, guess what acceptable usability is? For me it's 60 FPS+ on the target hardware, so if your game is simple, languages like C# should work fine. If it's very complex and uses advanced rendering techniques for special effects, highly detailed AI x 100, etc., C# may not be fast enough.
In a time where Dual Core CPUs have become the norm and Quad Core CPUs are already entering the mass market, I think your 60 FPS+ benchmark can soon easily be passed even by purely interpreted languages, provided that the language allows you to use all cores and you can parallelize your code. And that is exactly where platforms like .NET, Java and also Python have always been very helpful and supportive.
The only relevant question is how productive your chosen programming language and frameworks are; everything else is what Tyler Durden in "Fight Club" said about self improvement. ;-)