The iPad's share of the tablet business shot up to 68% in the first quarter of 2012, climbing more than 13 percentage points from 2011's fourth-quarter share of 54.7%, said IDC's Bob O'Donnell, program vice president for clients and displays.

At the same time, Amazon's share plummeted from about 17% in the fourth quarter of last year to just 4% in this year's opening quarter.

O'Donnell attributed the spike in Apple's share and the drop in Amazon's to several factors, including the U.S.-only sales of the Fire -- which tightly tied it to the U.S. holidays -- and the iPad's international reach, including in China, where the tablet was a hot ticket in that country's January holiday gift-giving spree.

"We expected to see a significant drop in Amazon Fire [in the first quarter]," O'Donnell said in an interview Thursday. "But honestly, the drop was a little bit more than we expected."

The dramatic shifts in share show that tablets remain a seasonal product, said O'Donnell. That includes the iPad, which saw its sales fall off -- even with the Chinese New Year at its disposal -- some 3.6 million units in the first quarter compared to the previous three-month period.