I've observed that women are quicker to say "Excuse me" than are men, even if they are passing by in the aisle of a store. There is no reason to apologize and I wish they wouldn't.
Walking around the store has become a peril, and dodging carts is the norm. I say excuse me to let others know I'm behind them so they don't back up into the cart and to assure them I can wait until they move.
I always say "excuse me" (or us since I'm with my kids) if I'm walking in a store aisle between the person and the shelves they are viewing. Given the width of the aisles, most times if someone is standing back at all to look at the merchandise, I have to walk through their line of vision.