With the exception of southern accents and a couple of others (New York?), basically all North American accents sound the same to me. I'd either have to listen carefully and juxtapose to be able to spot the difference or have the differences pointed out to me. I even have a lot of difficulty distinguishing between American and Canadian accents.

Contrast this to where I live in Belfast. Go a few miles south to Dundalk and the accent is utterly different. Go a few miles further south again to Dublin and once again the accent becomes totally different.

Granted, this may just be because I have more exposure to Irish accents than American accents, but I imagine the fact that English has been established in these places for significantly longer than it has anywhere in the US also plays a role.