It's a matter of scope. For bash pretty much everything is foreign, so it can only autocomplete if it get's some external source information for it, which usual

It's a matter of scope. For bash pretty much everything is foreign, so it can only autocomplete if it get's some external source information for it, which usually means someone must write/generate it. Powershell on the side is an object-orientated shell, and makes big efforts to pull everything into it's objectspace so it can use it's introspection-abilities to deliver as much information as possible about a command. Thus it can generate the neccessary informations for autocompletion on the fly. Powershell is more like IPython (with .NET as backend) then bash.