After digging around a bit I now see that this may be a larger problem than I first realized.
It seems that if you activate variable products, not only does the ability to set a single price for all variations disappear from the admin page, but also the "add to bag" and product price disappear from all the product scrollers, related items and upsells sections.
This makes sense because if a product is variable, I'm guessing the system doesn't know which variation to "add to the bag" until the user first selects a variation from the single product page. Also, the product scrollers don't know which price to display because the system allows for different prices for each variation.
The logical thing would be for there to be a setting in the Admin interface where you can set the product pricing as either a single price for all variations or a different price for each variation. Please tell me such a setting exists and that I just haven't discovered it yet. :-)