I think there are a few flaws in the original assumptions.
First, the 'Perl losing ground compared to' idea. A mature, well spread language, with just over 20 years of active development cannot have the same growth rate of a new one. It has nothing to do with market share or with spread of usage.
It's the same concept as giving full numbers to your incremental releases, it has no actual meaning.

Second, the GUI example. Tk is a portable, custom-widget based Tool kit, while .NET uses the Windows controls API. You can use that same API in Perl and have the same flashy bling Windows users can't appear to live without. It doesn't apply to Tk, nor to Ruby's better support of Wx.
Perl has a good support of Gtk and others, but even with a great support of any portable Tool kit, Microsoft will always provide better support for their proprietary tools.

The final issue is "good looks sell". Buzzwords also sell. Claiming your technology is "Business-standard, Enterprise service oriented for rapid, practical development" sells. It doesn't make a technology better when your NT Java-based server farm crashes every other week for garbage-collection problems.
A few years ago, Perl was the hype for web-development, then it was J2EE and its ilk, now it's Python, PHP and, Rails, and actual numbers be damned. If in a few years it will be Erlang or something similar, should that mean that Perl 6 needs to eschew everything and become a concurrent, functional language?