What I get from Jobs reply is that right now there aren't many product released using the USB3 norm.
When you look
at the list. You can see that there are only 116 products listed, of which only 31 are end-user storage products (counting HD enclosures).
So you could put USB3 in all the mac you want, but user would still have a hard time finding products, corresponding to their needs, using the norm.
The real question is will USB3 manage an industrial following before Light Peak is introduced?
Since Light Peak is made by Intel
(and thought by Apple in the first place) , they'll probably make it a standard on PC mother boards when it's ready, quickly and easily outnumbering USB3 capable machines.
Apple after creating and pushing the FireWire standard, that's still used industrially, is looking to bring another standard more robust and easier to use that will be able to handle every peripheral thrown at the users, from storage devices to external monitors.
And here is one of the interesting things Light Peak will be able to do for the professionals, right now if you want multiple screens you need multiple video cards but, if you only want to use one display, most video capacities are wasted if you can't use (like macs) SLI or CrossFire.
Then what about OpenCL capacities? As Apple has made clear with is continued use of old Core2Duo only for the benefit of having a OpenCL capable graphic chip, and their implementation of the norm in Snow Leopard, they feel that the centralized used of all the machine calculation capacities is a must have.
A standard like Light Peak would remove the need for graphic PCI cards to have out ports, directing every output through the PCI to the CPU allowing the full potential of the hardware to be used and controlled by the system.