Seen that mentioned a couple of times on here, but I don't really see that at all. The Emirates is a far more generic "bowl" type stadium, both inside and out, whereas the Amex has far more pleasing and original curves. The roofs of the Amex dip down almost to ground level on the north and south sides, the south in particular, which is something I've never seen at any other stadium, anywhere. Its unique.
The only thing that can draw a slight similarity is the white roof trusses. But even then ours are arches whilst theirs are just flat supports. I don't think the Emirates looks anything like the Amex.
Are they? they look exactly like ours to me. In fact the two stadia are very similar. Next you'll be telling me these two are nothing like one another....