This is a brilliant blog post.

What happens if you write to the address listed in the GPL?

https://code.mendhak.com/gpl-v2-address-letter/

I wrote to the address in the GPLv2 license notice and received the GPLv3 license

I was curious about the 51 Franklin Street address in the GPLv2 license notice so I wrote to them as they said

@Edent How is GPLv3 different?
And why did you get it in the mail?
If I want to get it, do I have to follow the same procedure?
Can't I just copy and paste?
@universish I didn't write the blog post. Please address your queries to the author.
@universish @Edent
GPL v3 is different from v2 several ways. It covers some additional situations that weren't anticipated in the original version, which makes it more technical. It also defines a lot of the terms whose definitions were assumed in v2, which makes it longer and more legalistic. Some developers, Linus Torvalds being the most obvious example, don't like v3 and have stuck with v2.