Don't forget the javaagent and the ability to instrument JVM. Event .NET/CLR doesn't have that (They have some low-level COM/Profiler API but boy that takes a lot of effort to work with).
Sorry I don't mean to hijack thread or anything like that but I work for AppNeta and we're on the APM field instrumenting various platforms. If you ever need an instrumentation tools for your full-stack infrastructure, check us out :).