Cleaning up description of GNU GPL in the index.html and changing the note in the gplv2 and gplv3 license pages

I made some minor changes to how the GNU GPL is described in the index.html page as well a change to the note on the GPLv2 and GPLv3 license pages stating that all source code files should state their copyright and licensing terms, which I think could make sense for all other licensing pages as well. 
What are you trying to solve for here?

> a copyleft license that protects free code from being turned into proprietary software

This gives the user less context then they currently get. It's describing the philosophy, not the practical implications for me as a consumer or a publisher. 

> protects better against DRM

DRM is jargon. The target audience should be a non-technical user.

> it's compatible with Apache 2.0.

Why is that vital to include on the home page? What's license compatibility? What's Apache 2.0?