When I fly Porter Airlines from Newark Airport (EWR) in New Jersey to Toronto, I show my passport as ID at the checkin counter. Same for United from Newark to Toronto.
But when I fly American Airlines from Laguardia (LGA) I show my passport as ID at check in, but then at the gate, I am verify my passport again at the gate, which they enter into the computer. To the point that they will not let you board until you do.
Flying out of Toronto, Pearson (YYZ) or Billy Bishop (YTZ) I have to 'show' my passport but do not have to have them enter any data about me.
Why the difference in approach? Is this an airline specific thing, or an airport specific thing?