I flew a 175 from MCI to PHL the other day and the seat map showed that the plane would be a reconfigured 175 but it was not. I had 2A and no one next to me in 2C, which was great. However, had someone already taken 2A when I did my seat selection, I would have annoyed to have to select another seat only to find, upon boarding that 2C was open. Obviously you could move, but if someone did that to me, I'd be annoyed ... petty, I know.
Oh and the flight attendant put her purse in the first available overhead bin too.