One anatomical point (and I'm no expert here, I'm basically regurgitating what I've read): lats stabilize the lower back when it's arched, so standing rows, your glutes and erectors are firing to keep you arched and standing up, so your lats should be assisting them. Seated, doesn't seem like you'd need the lats to stabilize teh lower back.
So more overall lat activation while standing maybe?