Actually Google Trends is a great measurement tool. You just have to know how to use it and understand what the measurements actually are ;-)

Checkout these two instead....

http://www.google.com/trends?q=python+scripting%2C+perl+scri...

http://www.google.com/trends?q=python+programming%2C+perl+pr...

In fact all languages have declined. Which isn't surprising because Google Trends is just showing you the frequency of these search terms used over time.

There is a lot more things to search for now on the web compared to 2004!