No surprise then that by Voyager's time, the policy had been quietly buried by Starfleet. Even after Chakotay got Cavit's job, never did he assert any authority to stop Janeway from beaming anywhere (and don't say it's because of Voyager's peculiar circumstances - it was plenty inconsistent, but for the most part the ship was run by Starfleet regulations). Likewise, Sisko (who had attained Captain's rank by then), Picard in the movies, and any given guest Captain were all seen routinely beaming into dangerous situations whenever they felt like it. I think only in "Nemesis" did Riker suggest that Picard going for a joy ride would be worth bringing up as a dumb thing to do, and Picard blew him off anyway.
Yup, somewhere along the line the "XO only on away missions" thing wasn't worth enforcing anymore. Stoopid cowboys.