Rich, that formula was easy 20 years ago because cuts, wipes and dissolves were invloved. Now that 30 layers of compositing with 3D, 2D and stop motion animation are easily possible, man 30 seconds of that and 3 cuts of talking head that make 30 seconds are two very different prices. This is why by the hour has been quite the norm for so long.
Now that it's easy to figure time involved before hand, flat rates are a great asset to those who can offer em. Big companies can't do this accuratly. It's why frustrated editors laugh or cuss after their bosses bid a project and make em work through the weekend. lol
Ever notice in big companies how the one doing the bidding is the one with the least experience?