If Amazon's Kindle Fire is so hot, why is it still in stock?

In a note to clients issued Monday, Hudson Square Research's Daniel Ernst reported on the results of a pre-holiday scouting trip he took to retail stores in New York and Connecticut over the weekend -- only a handful of shopping days before Christmas -- where he found "floor traffic up materially, but lines at checkout short."

Demand for tablet computers was strong, he wrote, with Apple's (AAPL) iPad maintaining its lead. Amazon's (AMZN) tablet sales, however, were a mystery.