And another: Fixes/Changes. If you rely on input filtering but you miss something, there's a bug and filtering doesn't work, or there's a new type of text that

And another: Fixes/Changes. If you rely on input filtering but you miss something, there's a bug and filtering doesn't work, or there's a new type of text that needs to be filtered (eg: a new tag added that didn't exist at the time), you have no recourse -- that text is already in the database. A software update can fix/change the output filtering, and since that runs at display time (when the vulnerability is actually activated), it can address it.