No.
It may surprise you but pull requests having nothing to with code review, they are just a formality.
To understand pull requests you have to understand character of the person that created git, Linus , the man behind Linux. He is not exactly the most easy going person, and he wanted a VCS that isolated developers rather than bringing together under one roof as SVN is doing. Its not very suprising when you consider the size and complexity of Linux kernel and his not so polite character.
Furthermore a pull request offers no practical advantage other than isolation, you can review any commit done directly to the repo and revert back the commits you dont like and open a discussion about it in the issue tracker. Github also offer several other tools, like comments on commits , gist for easy pasting of experimental code etc etc
And what makes pull request ever less uselful are branches, git�� already offers a form of isolation, you can create your own branch in the repo that wont affect the master branch, you can open then a discussion on the issue tracker and you or some other merge the branch to the master branch. Usually master branch is the unstable version anyway , an additional stable branch is usually created for the end users.
Also pull requests come with a big disadvantage , fragmentation. Because they lead to the creation of forks . That is not a problem by itself when the fork only contains a handful of commits but a fork can easily deviate without issuing any pull request back to main repo. Its similar to Squeak / Pharo situation, the fork becoming more popular than the main repo. And in the case on Squeak/Pharo is fine because the fork is only one, but a trip to github disneyland will reveal a hell of forks especially for popular repos. This can easily lead to "a war of forks".