And yet as far as I know no Canadian kids have choked, yet some American kids did. This has always been a point of confusion for me.
I haven't heard of any American kids choking. Three UK kids apparently did though, according to Wikipedia.
Basically the way our legal system works is that you have to define in legalese what constitutes a "choking hazard" and what doesn't (inedible substance of certain size in food), and then decide what to do with all "choking hazards" (don't sell them.)
Since the American legislative procedure was set up with the intent of making it difficult to pass laws, we try to aim for blanket bills and regulations that will solve any major problems, using definitions to aim for the target areas. For example, in Texas home-schooling is classified as a Private School, which means that home-schoolers get all of the necessary protection from the laws they do need without the State having to wrestle through 30 billion separate bills. Similarly, we're not going to try to wrestle through different bills for things like Kinder Eggs, just because they're funky exceptions to the rule.
It's a "for all intents and purposes" mindset, which can (and does) lead to bugs in the system (like no kinder eggs) but works reasonably well, for the most part.