I think I know the origin of this tax bill and what it is intended for.
Acquia - http://www.acquia.com/ - is a large firm that specializes in Drupal. A lot of the work they do is around setting up, configuring and maintaining Drupal websites.
While they don't produce the majority of the code that is in Drupal, they do provide a lot of services around it to consumers and other businesses. This is really a tax on VARs and other people who implement Drupal using their services.
I am sure there are a lot of other companies that operate in a similar space. While I don't like it, I can see the potential revenues to be drawn in through such a tax.