Intel's USB 3.0 controller running USB 2.0 devices on Z77

Hello,

I just tries out the new Z77 on a Gigabyte Z77M-D3H mother board.
What's the most exiting for me, is to try the first native Intel's USB 3.0 implementation.
I use USB 2.0 cameras backed by a Cypress FX2 witch is really sensible to the host controller you connect to. For example, I was enable to run my cameras on an Etron USB 3.0 controller.

On Z77, no problem, my cameras work like a charm... And even more, because I'm able to break the 480Mbps limit by controller.
To be clear, I was able to run 3 cameras on the same controller, using each 30MBps (240Mbps) of bandwidth !!

It seams like if Intel's USB 3.0 controllers running USB 2.0 devices will allocate 480Mbps for each of these devices. Is it true ?
If so, is it an USB 3.0 specification requirement or just the way that Intel implemented it ?
What are exactly the bandwidth sharing rules for USB 2.0 devices on USB 3.0 controller ?

Thanks in advance.
Ju