What about recruiters who are full-time employees of the hiring company?
I think a stronger restriction, namely "you should only post about positions which you will be personally involved with" would make this more even useful -- we don't need to be told every month that Google, Amazon, Microsoft, and Apple are hiring, but if tptacek (to take a local celebrity as a convenient hypothetical) posted that Starfighter was looking to hire a sysadmin then potential candidates would be able to ask questions and anticipate getting useful answers.