Well, Apple simply goes with the flow... Before Apple supported USB-2, there were tons of devices coming out for the new standard. And slowly, FW400 became a "second class" citizen in stores around the world. PCs had USB-2 on-board, but many PCs didn't have FW. For us Mac users, this meant to search longer for the right device (or not find a version of something for FW at all) or even paying more for FW-only or combo devices. Now that Macs have USB-2, this problem has been solved.
Apple hasn't pushed FW800 as much as they have FW400, and the market didn't simply pick it up as quickly. Also for most devices, FW400 and USB-2 are "good enough". And FW400 does not share the cables/connectors with FW800, which also hinders its deployment.
As for the iPods going USB-2: Same reason. They had to choose between FW400 and USB-2. For a while, they supplied both (as long as most Macs didn't have USB-2), but now that's not necessary anymore. Simple cost choice.