AU allows up to ten images at once, but there is a nice cadence to the Twatter limit of four at a time when telling a story. Also I notice a lot of people on AU only look at the first image and don't realise there are more; the bars overlaid are a bit too subtle.
personally, i prefer the ‘spread’ preview that shows all images attached, so that you know they’re there. maybe Koba@administrator can work in a new image preview to AU v2 :)