usb 3.0 interfaces?

with the speed increase of usb 3.0 (5Gb/sec)  vs 2.0 (480Mb/sec), why haven't mfgrs made some sound interfaces with that spec?

So why USB mixers 16bit here in 2012

Because 16 bits is sufficient for a simple mixer. 96db dynamic range is still better than any classic analog console. The benefits of 24- and 32-bit audio only come into play when you start applying DSP to the signal. Now, if you were doing everything inside the mixer including effects and automation (as opposed to doing all that in your DAW), then yes, you'd want a mixer with 24-bit capability.

Maarkr: USB3 is still quite new, so it will probably take some time before we will see any audio interfaces with USB3 introduced, if ever, especially as Thunderbolt is already for some time available on Macs and now becoming available on PCs. More likely to only see other devices with higher bandwidth demands using USB3, like disk storage devices of which many are now USB3. 

There are already high bandwidth audio interfaces in professional use connected via MADI transport through PCI and PCIe, and these will probably also be implemented on Thunderbolt (which implements PCIe) rather than USB3.

The main concern at this time is whether existing USB1.1/2.0 devices work on USB3 ports, as there have been some compatibility problems even though USB3 host controllers are supposed to support all USB speeds. But most (if not all?) computers with USB3 still offer USB2 ports as well.

bitflipper: Check your units/math. USB2 is 480 megabits/sec (Mb/s) like Maarkr wrote, not megabytes/sec (MB/s) which you wrote. Big difference.

And don't forget to subtract the overhead, and while you're at it, take account of the system loading and  latency.

Jim: I think you will find that most if not all of Intel's "7 series" PCHs do in fact integrate an xHCI host controller providing 4x USB3 ports directly and do not employ any 3rd party add-on for USB3.0, not just Z77. I do know for certain that H77 and B75 do.

So, I don't know why you say that some units won't work at all. Maybe you are referring to a particular motherboard implementation where the board maker added on a 3rd party chip in order to provide more than the 4x ports already available from the PCH? Or was it an incompatibility with USB2.0/1.1 devices?

Of course, AMD has integrated USB3 on some newer chipsets too.