My guess is that C# supports stuff that has no direct and fast implementation on the JVM. IIRC C# has unsigned primitive types, stack allocated objects etc. which JVM doesn't have.
I don't quite understand why that sort of methods should belong to array-class. Should array also have product-method? Average? Standard-deviation? Concatenating strings? Where should you draw the line?
The more I have thought about fully dynamic languages that don't allow any form of static typing information, the more I have begun to think that they are not very useful. Sure, polymorphism is nice, overloading is nice, but all of the programs I have written, have relied on some sort of typing discipline, be it dynamic, static or whatever. I can't imagine writing a useful function for which I wouldn't know what it's type is. Just because Java, C++ etc. implement static typing poorly, doesn't mean static typing has to suck when there are many languages that have inferred static typing, which in my opinion can provide best of both worlds.
EDIT: By "best of both worlds" I mean "concise code and the benefits of the program being well typed"