Hey Dan — I'm assuming you've moved on but I just found a bit of a work-around to this while researching the very same question and thought I'd share it.
While you still can't sort by list of Landing Pages by "Form" when looking to batch approve, you can sort by "last updated". Sort by most recent here. All landing pages using the form that you've just re-approved will be the most recent in this list, making it easly to select them all and approve.
Mike