Actually, there is something "disgusting" about requiring allies to "pay up" for effective use of the NATO terms of agreement.
What disgust me is that there is no such thing as "paying" to be in NATO. NATO is not a country club where you have to "buy" your right to participate and then pay green fees every time you play. It is a political treaty for defense where countries undertake some obligations to one another - none of which is financial as there is no such thing as a NATO annual fee - except to maintain the treaty headquarters' building and upkeep. There are also some specific contributions that are negotiated on a piece by piece basis.
For instance, the NATO AWACS fleet is operated on the basis of specific undertakings by the nations who elected to participate to provide so many trained personnel in positions x, y and z and to provide for their portion (as agreed) of the operating costs. Similarly, before the fall of the wall, there were specific number of escorts that some NATO countries (including Canada) agreed to keep available for the protection of convoys in the Atlantic. Then there were specific formations that some countries agreed to make available for the defense of Europe - The British Army on the Rhine, Canada's brigade as part of it, etc.
There was no actual amount of money any member country had to "pay" to "NATO".
How much money countries spend on defense is up to them and based on their individual view of their requirement. The US is NOT, repeat NOT, spending what it is spending on defense BECAUSE of any NATO undertaking but because that is what the US considers necessary for the defense of its own interests around the world. The 2% undertaking is just that: an undertaking by NATO nations to spend that much on their own defense - not on aggregate NATO defense -, because it sends a signal to potential enemies, not because it contributes to collective defense. Lichtenstein could spend 10% of its GDP on defense and it would make no difference whatsoever to NATO's collective defenses, whereof Canada's contribution can, for all practical purpose, be entirely used in collective defense because there are little to no threat against our own territory, even if it only amounts to one percent of our GDP.
BTW, Brad, I am sick and tired of people (even in these fora) always presenting Canada as a "free rider". Canada has the seventh largest NATO defense budget in terms of spending in actual dollars. Who beats us: the US, the UK, France, Germany, Italy, Poland. Every one of those countries has a much larger population than Canada and, except for Poland, has a higher GDP. Moreover, every one of those countries needs to spend on their own defense as a deterrence from invasion - not necessarily as a contribution to alliance collective defense - whereas Canada needs very little in terms of deterrence and as a result is mostly contributing to collective defense with its spending.