Where research firms like Gartner, IDC and NPD saw anemic single-digit PC sales last quarter, Canalys saw what it described in a report issued Wednesday as “strong PC industry growth of 19% in Q4 2010.”

The difference is that Canalys, unlike those other market research firms, includes tablets like Apple’s (AAPL) iPad in its definition of a PC.

By that measure, Apple’s PC sales grew 241% year over year, catapulting the company into third place in worldwide shipments, ahead of Dell (DELL) and Lenovo (LHL.F) and behind only HP (HPQ) and Acer.

“Pads gave the market momentum in 2010, just as netbooks did the year before,” said Canalys Senior Analyst Daryl Chiam. “We are encouraging vendors to plan for the future and not to remain stuck in the past.”

“Any argument that a pad is not a PC is simply out of sync,’ he added. “Apple is benefiting from pads, just as Acer, Samsung and Asus previously did with netbooks. The PC industry has always evolved this way, starting when Toshiba and Compaq rode high on the original notebook wave.”

Below: What worldwide PC growth divided by regions looks like when tablets are included.

You can read the full report here.

[Follow Philip Elmer-DeWitt on Twitter @philiped]