You missed something I said before. The torque converter also offers a "gear ratio". According to wiki this torque multiplication ranges from about 1.8:1 to 2.2:1 [ame="http://en.wikipedia.org/wiki/Torque_converter"]Torque converter - Wikipedia, the free encyclopedia[/ame]
So take your automatic ratios and multiply at least first gear by about 2:1. That makes your first gear range as low as ~20:1. Now you only get that 20:1 when the car isn't moving. As the TC speeds up that ~2:1 becomes 1:1. So the TC has a much lower "first gear ratio" when you look at how many times the engine torque is multiplied. I use quotes because unlike the manual where both torque and speed are multiplied, the TC only multiplies torque, not speed.
Now in my example I only talked about first gear just as the car gets rolling. With older 3 speed and even 4 speed autos (or even the VERY old 2 speeds) you are often running the TC in some range where it isn't delivering 1:1 input to output speed and toque. In other words, it isn't locked up. Thus when going up a hill in top gear your net ratio isn't just the gear ratio * final drive you listed. It also might included a 1.2:1 torque multiplication in the TC.
When GM first started experimenting with automatic transmissions they initially had a 3 speed with a hydraulic coupling that offered no ability to multiply torque. It was effectively a viscous coupling. That transmission was a 3 speed design. When they first started using a TC they had only two forward speeds. Still, with only two speeds that TC equipped auto had a greater total torque multiplication range than the 3 speed auto. This is why for a long time a 4 speed auto could tow just as well as a 5 spd manual and wouldn't rev any higher on the freeway. The TC effectively gave the car an extra gear ratio at least when it came to how much torque (not speed) the engine could apply to the ground. Basically, the TC allows a gearbox with a narrower total ratio range to behave like it has a larger range.