Actually my initial motivation for developing pss was Windows. I had to use Windows at work at the time, and installing Perl just for the sake of ack was pain. ack also needs an additional module from CPAN (for console coloring), so double pain.

Python, OTOH, is always one of the first I install on every machine that doesn't have it :) pss requires no installation, no additional modules, just Python.

Aside from embedded/routers and Windows machines, it's few and far between. At the very least you're going to have something ancient like Perl 5.6 or 5.8 installed.