Neither 4-pin FW nor USB 1.1 will charge...
Yup. In order to charge an iPod, you either need 6-pin FireWire or USB 2.0. So if you buy a new iPod, you'll need to get a charging adaptor, in addition to the FireWire cable. I'd recommend getting the FireWire cable, 4-pin-to-6-pin adaptor, and FireWire wall brick charger.
The technical issue is that USB 1.1 is limited to 500mA of current per port, which isn't even enough to charge the mini. USB 2.0 can provide more power per port (don't know the exact limit, but it's at least 1A,) which can charge it. 4-pin FireWire is missing 2 pins for one simple reason: It doesn't have the power pins.
I have a 2.5" bus-powered USB hard drive case that uses an interesting method to get around USB 1.1's lack of power. If you are plugging it into a USB 2.0 port, it gets enough power to run just fine. But if you want to plug it into a USB 1.1 computer, you have to use the (included) Y-adaptor. It draws power only from one USB port, and both draws power, and makes the data connection, from a second. (The power-only plug is also a data pass-through, so you can have another device plugged in as well.) It's an interesting compromise for running a high-power device on a low-power USB 1.1 computer. Too bad Apple doesn't use such a method. (It is a good geek compromise, but I guess it is a bit cumbersome for the average Joe.)
I think it sucks that Apple is removing FireWire as a standard interface from the iPods. With the shuffle, it makes sense. But not for the rest of the line. I suppose the iPod is moving from 'Apple cool' to 'commodity MP3 player', so Apple's got to maximize profits any way they can.