A story first reported by SemiAccurate, and later picked up by Apple Insider, suggests that Apple has little confidence in Nvidia that it can supply enough 28 nm Kepler graphics chips to support Apple's demand. Apple apparently has already made the decision to dump Nvidia for "a large number" of notebooks and may only use Kepler in a limited way, potentially only for the high-end. Given the fact that Apple sells about 3.6 million notebooks per quarter, this may - if the rumor is true - hurt Nvidia.
The rumor further suggests that Apple now intends the graphics capability in its notebooks mainly via Intel's Ivy Bridge processors, which somehow fits to the rumor that Intel has delayed the introduction of Ivy Bridge due to a large order from Apple that may be connected with the Kepler supply issue.
While all of this information is unconfirmed and neither Apple nor Nvidia will comment on it, we know that Apple is paranoid about eliminating all variables its component supply and make sure that it has enough parts to ship all the products it can. If Nvidia cannot satisfy Apple's demand of potentially several million graphics chips per quarter, it is reasonable to assume that Apple would dump the company in this round.