Apple (Nasdaq: AAPL) has been pushing its iPhone 5C, the lower-cost version of its latest handset line. Some market watchers have been questioning the move.

AllThingsD today said that it might be due to supply issues for the upper-scale iPhone 5S. ATD cites several sources at U.S. wireless carriers in saying that supply is less than expected. One commented that they will have grotesquely unavailable inventory.

One source from a second carrier was said to be disappointed in the inventory, but demand might be less than initially though as well. More customers have been attracted to the brightly-colored iPhone 5C.

At launch, the iPhone 5S will be carried n AT&T, Verizon, Sprint, and T-Mobile.

While Apple has shifted focus to the lower-cost iPhone 5C, maybe the move isn't because it wants to, but because it has to.

Shares of Apple are up 1.4 percent.

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