Hi,
I'll admit right away that this question has no real practical problem 
behind it, it's just out of internal consistency:
The mean() function accepts a list and then averages across the members 
of the list (and returns a series of per-obs-averages).
In contrast, the pmean() function doesn't have this second use, it only 
accepts one series (as does mean). Any particular reason why not?
The same goes for pmax(), pmin(), psd(), psum(), and perhaps also 
pxsum(), I guess.
thanks,
sven