Despite having enthusiastically adopted Intel's Thunderbolt technology - most recently in its refreshed MacBook Air and iMac models - Apple is reportedly still mulling over adding support for USB 3.0 to future product lines.
Word has it that the manufacturer plans to make a move in the USB 3.0 direction, before Intel integrates USB 3.0 into its own chipset offerings, and apparently sees the standard as an option to providing connectivity for devices not requiring the tremendous bandwidth benefits of Thunderbolt.
There's also the claimed pricing-benefit of adding USB 3.0 support, to complement the presence of Thunderbolt technology. Reports indicate that USB 3.0 host connectors are now priced within the $2 to $3 US Dollars region, when purchased in suitably large quantities, compared to up to $15 US Dollars for the Thunderbolt variety.
This means that the addition could be made at, seemingly negligible, cost to Apple.