Does Drew prefer email, or prefer not doing more work than he already does?
A pull request, literally, need only be moving code from one repo to another.
The signaling mechanism etc. are not and shouldn't be specified by git. How code moves around should be dictated by your organism, copyright, access levels, not some guy's interpretation of what "pull request" means.
That means, yes in some instances there is no 'master' version of the software, there are multiple flavors with different release characteristics.
E-mail I suppose is an adequate communication medium, if people want a specific review mechanism and triggers adding one to source hut (assuming FOSS) shouldn't be hard, perhaps the authors intention is to make it difficult to regress to a centralized model.
Email-based review tools are built-in to git. git format-patch, send-email, am, imap-send, etc.
Git only comes in play when the review is finished, and it's time to commit the changes to your repository. So I claim that git does not have tools for reviewing pull requests or patch sets, only for managing them on either end of the pipeline - creating them, sending them, and applying them.
Which, to be clear, is not a criticism of git, as I do not think git should grow such review tools.
Isn't that what discussion board is for? I agree that this particular topic is not life-and-death important, but still worth discussing, IMHO. If you think otherwise, just walk away, you do not owe anybody anything.
It matters because where you assign your responsibilities is the difference between spaghetti code/architecture and a well designed one. If you think this is nitpicking, I encourage you to (re)view the general sofware concepts of cohesion and coupling.
(Part of) gits success is it is a tool focused on doing one thing well - I believe Linus is on record as saying the other tooling (commercial/svn) largely failed because they were not really focused on source control i.e. patch management. Its part of the reason he constructed it in the first place, the tool he was using was overcomplex and bad at doing simple things.
Github's success until this point has been largely that it focused on building review infrastructure. It's based on git, giving it flexibility akin to being based on e.g. http, but it's core is review and facilities in support of that e.g. code search. It's a very particular type of review aimed at a specific audience, but it's not git, nor should it be.