Car RAMROD, I think of the main issue is that the BOM Website does put up the TAFs, but are they necessarily the most current ones? How often do they update them? I know it seems like in our world of tech they should just be the latest ones all the time but that's not necessarily the case, it could just be a simple web page someone does up a couple of times a day as a reference.
The idea is that NAIPs is meant to give you the most up to date ones, it's assured basically, if you use it they'll be the latest, I'd suspect the ones on the BOM website are published but aren't necessarily updated as soon as new ones become available. It's why they give you that warning when you go to the site, they don't want the extra effort of putting in place the coding, personnel etc... required to duplicate what is essentially done by ASA.
This is the hazard that arises from using them and is the reason why they are a "Provider" of Information but NAIPs is meant to be our "Approved Source".