1) USB 3.0 isn't needed for a DAC as digital audio isn't too terribly demanding on bandwidth. Total bandwidth required for a 24bit 96khz stream is about 4.4 Megabits/sec. That's well under the 11Mbit/sec theoretical bandwidth (figure roughly 7Mbit/sec real-world bandwidth) provided by "full-speed" USB 1.1.
2) Even though the WM8741 can accept 192khz and DSD, I can guarantee you the licensing fees and extra circuitry required to decode the HDCP would have pushed the DAC past it's current sub-$500 price point. Accepting encrypted DSD isn't as simple as tacking on a HDMI port to a DAC (I wish it was though, it'd be great for the DIY crowd).