Just to add to Sweden's answer, the technical way to state the time of X months on CIC website is: 80% of cases were completed in X month or less.
So basically the time stated is a worst-case scenario for 80% of applications. Most people get the "or less" time, but some people unfortunately fall outside the 80% and get times way over what's stated.
For a better indication of the "average" time from your visa office, it's better IMO to look at the 50% stats which you can see by downloading the Open Data excel sheet amikety linked to above.