I'm sure there are substantial compatibility layers in perl, but I have the feeling those are mostly resolved during the compilation of your perl binary. At least, that's what I gather from the fact that XS modules built against, say, 5.6 aren't binary compatible with 5.8. I don't think perl has the runtime issues that Windows does. That's the big advantage of having source code: you can optimize the build for your platform.

That doesn't detract from the complexity of the source code, of course, but it doesn't imply that perl is slow. IMHO.