Hyok Ki Chung thinks so. Quoted on Macintouch, Chung analyzes a Korean news article:

While browsing a Korean Mac magazine site, I found this interesting article. It's about the USB 2.0 controller chipset on [Power Mac] MDD 1.25 and 1.4 motherboards. According to this article, the controller is made by NEC, model number uPD720101. The article is in Korean, but basically what it describes is the NEC USB 2.0 controller. It also mentions the driver, saying that Mac version is not available yet. It looks like we already have USB 2.0 built-in. I guess it's just matter of time. Hopefully Apple will add the driver to an updater soon.

Obviously, Apple doesn't want to really push USB 2.0 right now, not when its own FireWire technology is picking up more steam, and the second iteration of that technology, FireWire 800, has hit the market on just-released systems. Perhaps I have just bought the Apple line, but USB for me is for small peripheral usage: keyboards, mice, my CF card reader, my little Canon scanner that barely gets used. For the "heavy lifting"--my external drives, tape backup, iPod--FireWire is the way to go. Not to mention that you can't use USB, 1.1 or 2.0, to boot a Mac as an external drive to another Mac, better known as FireWire Target Disk Mode. UPDATE, 9:50 pm: Ric updated with follow-up from Kevin Purcell:

But examining the Apple Hardware Developer notes [Power Mac G4 Developer Note], you can see that these PowerMacs only expose two USB ports which means the USB 2.0 port in the chip is not connected to any PHY or external connector on the Power Macs. Only the low-speed/full-speed ports are connected. I don't expect to see a software update. Apple probably just bought these because they meet their spec (an OHCI controller) and they needed a 2 or 3 port USB solution.

So, maybe wishful thinking...