From JKR:
The 29% statistic was for the entire electorate not the popular vote. So for example, in 2011 the Conservatives won a "majority" government with the votes from just 24.3% of the electorate and just 39.6% of the popular vote.
I can't speak to elections in Quebec, but I can speak to elections in BC. It's true the NDP won a majority with a lesser percentage of the vote than the BC Liberals. The voters were so overjoyed with that result that in the next election they reduced the NDP to two members, and handed the BC Liberals majorities for the next seventeen years. It's also true that at the time everyone remarked on how unusual it was that a majority government could happen with fewer votes than the next party in line.
As to the 29% thing, you can't count votes that are not cast. The best you can do is assign uncast ballots to parties in more or less the same percentages as cast ballots. Or just say that people who didn't vote don't care what the result would be. Your method of arriving at the 29% is a bit of sophistry.