Typically, Star columnist Thomas Walkom blames the NDP for the Conservative majority: http://www.thestar.com/news/canada/article/984534--walkom-ndp-surge-gave-conservatives-coveted-majority.
He cites no data for this. The data don't support this claim.
Nationally, the Liberals fell 7 points in the popular vote from 2008. The NDP was up 13 and the Cons 2.
In Ontario, the popular vote deltas are:
That is, Green votes went NDP, and Liberal votes divided between the Cons and NDP. If the Liberals had been able to hold their own right flank, they could have denied the Cons a majority.
In 2004, the Liberals had 45 percent of the vote in Ontario and the Cons 32 percent. In 2011, the Cons got 44 and the Libs just 25. This is a slow and steady transfer of vote from Liberals to Conservatives. That is hardly the NDP's fault.
And there are some ridings where you can argue that Liberal votes weakened the NDP enough to hand the riding to the Tories: Bramalea-Gore-Malton, Sault Ste Marie, and Essex in Ontario, Megantic-L'Erable, Lotbiniere-Chutes and Montmagny-Riviere-du-Loup in Quebec, and South Shore-St Margaret's in Nova Scotia.
Ultimately, the Cons got a majority because they got a lot of votes, strange how that sounds. Consider the English Canadian popular vote:
which is not just a majority, it's a landslide.