If the building inventory model is a single db table for all buildings, then such a query would cause locking and timeout stuff. This would happen whether it's happening by the forums or the game client--I think that's Nerdy's point.
@Noahhh! think about an Excel sheet that can only be viewed when nobody is editing it. If you had one sheet for every housing transaction (ie accessing T, putting shit in, taking stuff out), everyone else would need to wait until that command is done. Gang banks are probably on their own "sheet" and not nearly as frequently accessesd. This is entirely guessing on my part, but probably why the discrepancy exists between inventory transactions and banks.
My point is that if you materialize a view of that table on a periodic basis (such as after a hard restart once a day), then queries against the view would not cause locking/time-out inventory fetches for in-game players. It would consume processor resources like any other query and add disk space duplicating information. Some people look really negatively on that.
But, to play devil's advocate, putting in a once-a-day view would create the precedent that people can see building transactions and then staff would get bugged about "WHY ISNT MY SHIT SHOWING UP IN THE LEDGER I PUT IT IN 30S AGO WTFBBQ!" so I get not wanting to do that, either.