Gartner says the growing appetite for tablets like the Apple iPad is cutting into sales of “mobile PCs” like laptops and netbooks. The research firm has lowered its forecast on PC shipments for 2011 and 2012 due to weakening demand for laptops and netbooks.

“We expect growing consumer enthusiasm for mobile PC alternatives, such as the iPad and other media tablets, to dramatically slow home mobile PC sales, especially in mature markets,” said George Shiffler, research director at Gartner, in the firm’s report. “We once thought that mobile PC growth would continue to be sustained by consumers buying second and third mobile PCs as personal devices. However, we now believe that consumers are not only likely to forgo additional mobile PC buys but are also likely to extend the lifetimes of the mobile PCs they retain as they adopt media tablets and other mobile PC alternatives as their primary mobile device.”

Gartner had previously forecast growth of nearly 16 percent this year, but now says growth will be just 10.5 percent in 2011 on global PC shipments of 387.8 million. For 2012, Gartner reduced its forecast from 14.8 percent year-over-year growth to 13.6 percent on shipments of 440.6 million units.

Until recently, consumers were drawn to netbooks and laptops for their portability, but the devices are heavier than tablets and do not offer the same battery life as devices like the Motorola Xoom. Gartner believes that these limitations are causing consumers to turn away from laptops in favor of tablets, which are more portable.

“All-day untethered computing has yet to materialize, and that has exposed the ‘mobile’ PC as merely a transportable PC at best,” said Gartner’s report.

Gartner said a bigger issue was that consumers are adopting a “wait and see” attitude on planned PC purchases until they could test out the performance of new tablets coming to market over the coming months.

Sales of laptops to consumers are expected to grow less than 10 percent per year between now and 2015, Gartner said. The sale of laptops to businesses is expected to post double-digit growth through 2012 as companies replace aging computers, though some replacements are expected to be delayed as the enterprise market considers tablets as a possible substitute for PCs.