Apple acquisitions suggest hardware sales concerns

Apple has acquired book recommendation service BookLamp, and it's expected to close a deal to buy podcast app Swell, possible signs that Apple's smartphone and tablet sales are expected to level off.

Quarterly tablet sales have already fallen, according to NPD Research, forcing Apple to explore revenue streams from products other than hardware, according to Jon Swartz, USA Today's San Francisco bureau chief.

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With Apple's Booklamp purchase, which was estimated at between $10 million and $15 million, the tech giant acquires book analytics that could improve its existing iBook search functions and recommendations.

The $30 million Swell acquisition would let Apple offer listeners personalized podcast playlists.

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Apple's recent buying spree amounts to an admission from the tech giant, under the auspices of Tim Cook, that it should no longer insist on developing new technology on its own, according to Swartz.

"It's decided it's not going to invent everything. It's going to acquire companies that are good and useful to it ... They realize they can't do it all themselves, and they have to reach out to others and just bring them in house," Swartz told CNBC.

In May, Apple announced its plans to buy Beats headphones and streaming music service for $3 billion.

—By CNBC's Althea Chang