The GPL is a completely different beast. First of all it does not govern the usage of software, but its distribution. It does not matter that you don't have to click through it when downloading GPL'd software, because it's only important when you want to distribute software. And in that case the default under copyright law would be "you don't have any right to distribute". The GPL grants you the right to distribute the software under specific conditions. So when making GPL software available for others you can either agree to the GPL or you are simply in violation of copyright.
Secondly, the "this or any later version" is again quite different. It allows you to distribute the given software under the current or any later version of the licence, but since you have the choice of which version to use, a new version cannot retroactively restrict your rights (e.g. if GPLv4 doesn't allow you something that GPLv3 does, you can simply keep distributing under GPLv3 if the original software said "GPLv3 or later"). As long as you comply with the version that you choose when distributing, you're fine. I don't think any court would find a problem with that, as you can't be surprised by someone else retroactively reducing your rights.
Not really. If you're not redistributing then you explicitly don't have to accept the GPL and may not be bound by it. If you are redistributing, then either you read and accepted the GPL or you're breaking the law. Redistributing copyrighted work is not "legal by default" the way clicking a link on a website is.
>This or any later version? Check.
The standard language is "or, at your option, any later version published by the Free Software Foundation". There is no claim there that the FSF can unilaterally change the terms.
The only concern I can see for free software is that "This software is distributed as-is without warranty" notices might not be valid if they're not prominent enough and the user isn't forced to click-through before starting the program.
