That's not accurate. In fact, in the .NET 2.0 timeframe the opposite was the case (the 64-bit JIT would fail to honor the IL tail. prefix in many cases, though it would also make tail calls in other cases even when the prefix wasn't applied)[1]. But as of .NET 4.0, both platforms honor the tail. prefix except in a very limited set of circumstances[2] (e.g. calls from untrusted code to trusted code).

As far as I know, F# is the only reasonably popular .NET language to emit the tail. prefix, though[3].

[1] http://blogs.msdn.com/b/davbr/archive/2007/06/20/tail-call-j...

[2] http://blogs.msdn.com/b/clrcodegeneration/archive/2009/05/11...

[3] http://blogs.msdn.com/b/fsharpteam/archive/2011/07/08/tail-c...