The WATIR people are doing an outstanding and elegant job of this in Ruby. There's no reason it couldn't be done in Perl, but no one has yet, at least at the level of elegance and sophistication demonstrated by WATIR.

Well, there is SAMIE and Win32::IE::Mechanize.

Personally, I'm not as certain as you are that Ruby isn't a critical part of WATIR's success. From what I have seen people find it much easier to move from WAITIR to more general Ruby code than from Perl testing frameworks to more general Perl programming.

Much as I love Perl it's been my experience that people find learning Ruby easier.