It's because highschool in Quebec is only 5 years and not 6 like in the other provinces. So you actually do the same number of years, but it's divided differently. If you did 6 years of highschool outside Quebec and choose to do post-secondary there, then you choose to take on that extra year... but the tuition in CEGEPS is non-existent, and it's lower even at university level than other provinces, so in a way, it all balances out...