Having a copy that you can access locally is great, but there are advantages to having it online.
First, it means you can navigate to it by googling "bootstrap 2.0 documentation". If you are using five JavaScript libraries, it can be annoying to have to find the folder for documentation for each library.
Also, you might not even have the documentation locally. Another developer might have set things up and they might not have checked the documentation into version control.
Not to mention that any old tutorials, blog posts, wiki pages etc -- now link to 404 land.
While it would be great if everyone could just magically upgrade, if you've spent a lot of time wrangling some content management system to the "old" bootstrap, you're more likely better off fixing bugs in that site, than upgrading and hoping nothing breaks.
If it's supposed to be used as a framework, I'd say it's common courtesy to provide the old documentation for at least a short period. It's not that hard, see eg:
First, it means you can navigate to it by googling "bootstrap 2.0 documentation". If you are using five JavaScript libraries, it can be annoying to have to find the folder for documentation for each library.
Also, you might not even have the documentation locally. Another developer might have set things up and they might not have checked the documentation into version control.