Most taxation is based on percentages. The reason the upper half pays more is because they have more. Percentage wise, they are pretty close, but gross dollars is higher. You pointed this out earlier.
In 2005, the top 30 percent of families earned 60.3 percent of all income in Canada and paid 66.3 percent of all taxes.
The bottom 30 percent earned 7.8 percent of all income and paid 4.3 percent of all taxes.
What this shows is that the wealthy pay slightly higher taxation levels. But what you fail to consider is the effect of sales taxation. Taxation based on non-neccessity spending is always going to lean harder on the wealthy because they have more disposable income. Whereas, lower income Canadians spend a far greater percentage of their income on neccessities and thus pay less in taxes.
In fact, I was always under the impression that the top tier wealth earners in fact paid more (percentage wise) in income tax than lower income earners. What you've shown me here is that I was wrong in the opposite direction. That the wealthy in fact pay very little more (as a percentage of their income, which is the important part of the equation) than what the lower income earners pay.
Also, as Kreskin pointed out, there are plenty of corporate tax strategies that allow high income earners to back out of paying almost all of their taxes. Because of the way tax law is, it is entirely possible for people making way above the national average to collect a GST rebate cheque. As such, it is difficult to take these stats at face value, and they must be taken with a grain of salt.