I agree with you that the docs are out of date.
I think the reason that the newest (Artem's version) is not in the plugins database is because he did not choose to put it there. I don't think anyone else would be comfortable adding it, since that is more appropriately the developers choice. I had some correspondence with him about it last year, but it appears that he prefers to keep up his github site instead of publishing in the modules database. His github site is commented, and he has more projects on it than attendance.
With respect to Dmitry's version, it still resides in the old plugins and modules database, but as far as I know, is no longer being kept up. Of course as we move further and further from Moodle 1.8, the less likely it is that people will want to install that particular version. In our case, we were using a REALLY old version, not wanting some of the extra features he put in later.
As far as I can see, the release notes for Moodle 2.3 do not include attendance, so it won't be in core any time soon. Perhaps you might want to direct message Artem and ask?
Perhaps the best way to deal with the docs situation is to find out how to open up a new page that focuses on Moodle 2.x attendance. In that case, I think the only module would be Artem Andreev's. Would you be willing to get it started? We are just now moving to Moodle 2.x, so I haven't had any experience with the new attendance module. I can ask Helen or Chris Collman about it.