As someone who is from the True North, I have to admit to being guilty of this... I say "sorry" a lot, and I honestly don't even realize it most of the time unless somebody points it out to me. It's like a verbal tick or something, but even though it's definitely more of a habit than necessarily an apology or admission of fault, it's not out of any sense of indifference to the situation itself - I can truthfully say that, at least in my own case, it does come from a genuine desire to be polite.
There are three types of contexts in which I know I will use the word sorry.... I know this because it's been pointed out often enough to me (when I'm in the USA and somebody says something, I usually joke about it and say it's because I'm Canadian), and I've analyzed the situations enough to isolate three specific categories, and how a person who is Canadian might be meaning the term.
The first type of "Sorry" is when I am genuinely admitting fault or being apologetic. One can usually, from context, determine if I am meaning this kind of thing based on whether or not I actually have anything that I probably could be apologizing for. If there's nothing there that makes any kind of logical sense, then it's probably one of the other two types.
The second type of "Sorry" occurs quite a lot in social or public situations, and I've noticed that I use it as kind of a synonym for "Excuse me", or else as a means to gain the attention of somebody.
The third type of "Sorry" also occurs a lot in social situations... and it's this one that I've noticed myself being guilty of. Less of an apology or admission of any kind of fault, it is actually an expression of willingness to defer my position to anyone who might be around me. One could think of it as a kind of pre-emptive apology of sorts... not because I necessarily expect to do something that I should be sorry for, but because if even the mere possibility might exist, I am only saying that I don't want to engage in such conflict, and will yield to others.
Sorry, I'm Canadian.