To include the iPad, or not include the iPad? It makes a big difference in notebook market shares. (Source: Deutsche Bank)

Most calculations of market share in the portable computing arena don’t include the iPad, which they consider a tablet and not a traditional computer. But because tablets seem to be cannibalizing computer sales, it’s not a stretch to include iPads in those tabulations.

Based on the line graph above, the notebook landscape changes drastically when iPad is included.

Deutsche Bank analyst Chris Whitmore calculated global notebook computer sales up until the second quarter of 2011 in a note to clients. Not including iPad sales, Apple ranks last, saleswise, as a manufacturer. Including the iPad, Apple soars to snag the top spot.

Whitmore’s note included stats about the top six notebook vendors: Acer, Apple, ASUS, Dell, HP and Samsung. The top two overall vendors for most of the time period, HP and Acer, have had generally downward trending market shares since second quarter 2010, which is right around when the original iPad debuted.

It’s been pretty clear that the iPad has been eating into laptop sales for a while, and this graph corroborates that. But compared to Whitmore’s calculations in 2010, Apple’s market share including iPad sales has actually gone down slightly, from about 25 percent to 20 percent. Does this mean that all those copycat tablets are actually edging in on the iPad’s market domination? Lenovo’s three recently revealed tablet offerings look to be pretty good Android contenders against the iPad, while others like the Samsung Galaxy Tab have had decent sales but still don’t make the mark. And according to Digitimes, iPad sales are expected to rise 55 percent in 2012, while non-Apple tablet shipments are expected to jump 134 percent.

“Within the tablet market, the iPad remains the gold standard as competitors struggle for mind-share and traction,” Whitmore says in his note — which must help explain why the iPad is the only tablet included in the second quarter 2011 calculation, when many of the vendors now have tablet models available. He also sees Apple snagging an even larger piece of the pie as the back-to-school season sets in and the Microsoft/PC ecosystem is “relatively stagnant.”

The iPad is very clearly still Apple’s prizewinning stallion in the portable computing department. Even with innovative competitors popping up, it’s going to take a lot to unseat Apple from its dominant position.