Requiring the use of priorietary software to access and discuss it is a problem, and requiring complicated software is not that good either, but it is also possible to use open protocols with multiple software.
(In the specific case of GitHub, they had previously allow viewing files without needing JavaScripts; that has changed now, but the data is included as JSON data within the HTML file, so I was able to write my own much shorter script to substitute for theirs. Of course, that does not help much if you do not have that script, but you can still use the git protocol to download the files, or to use the API (the form for creating a new repository has stopped working on my computer, but I have been able to do so by using the API).)
One thing they do not mention is NNTP, which I think can be a helpful alternative than mailing lists (although you can also have multiple interfaces for the same messages).