Piper Jaffray analysts Gene Munster and Douglas J. Clinton think that in the long run any cannibalising of Mac sales by iPads will pay off because by 2020 the market share of tablets will be great than PCs, and the iPad will have the biggest share. 

The analysts predict that by 2015, total tablet sales will have reached 301 million units, and of those, 176 million will be iPads. In contrast, by 2015 the PC market will have reached 484 million units. And by, 2020 tablets could take over sales of all PCs. 

"Thus, the gap will be significantly closed between tablet and PC unit sales by 2015. We believe tablets could overtake sales of notebooks by 2015 and total PCs well before 2020," states the Piper Jaffray report.

The analysts said: "We believe Apple maintaining its majority (60 percent plus) market share in the ultimately larger tablet market is more important than meaningfully increasing single-digit market share in the PC space," despite the price of Macs being two and a half times higher, wrote the analysts, according to a eWeek report