US owners of iPads tend to be older and richer than people who buy rival tablet computers, according to a study released on Friday by NPD Group.

The industry trackers Tablet Adoption and Insights Report showed that more than 40 percent of iPad owners had household incomes of $100,000 or more with only 26 percent of those owning non-Apple tablets rising into that bracket.

Apple's cheapest iPad costs $499. Most of its rivals offer cheaper devices with Amazon's Kindle Fire selling for just $199.

As tablet computers get more mainstream, the demographic disparity is lessening due to younger people with lower incomes getting the devices, according to NPD.

"As the demographic of the tablet owner continues to change the tablet market is beginning to take on a new role," said NPD vice president of industry analysis Stephen Baker.

"We are seeing some of the tasks traditionally performed on devices, such as PCs, now being performed on the tablet."

Despite talk of entering a "post-PC era" defined by the rule of Internet-linked mobile gadgets, the majority of tablet buyers said they still felt the need for laptop computers, NPD reported.

"Even as consumers increasingly use tablets for tasks that were once exclusively done on their PC, they continue to plan new PC purchases," Baker said.

"Usage is still evolving and most people, being inherently conservative in their device outlook, continue to hedge their bets on their device preference by planning to maintain an array of products to afford them maximum flexibility."