That makes sense.

1) One-ways from Canada to the US can have Canadian plates if it's a border city, where Canadians doing the reverse one-way need a car with Canadian plates. One-ways deeper inside the US need American plates, since the car can not be rented locally, and likely won't have a one-way back to Canada.

2) A former Hertz employee on FlyerTalk once said that cars that are rented at some point in the NY metro area tend to have something wrong with them. It could be the ever-present potholes whacking the alignment, heavy usage by a large number of people, grime from salt and snow, etc.