No... /shout does not cover the whole zone. I'm not sure of the exact measurements, but shout covers 6 x the distance of a /say. A /say from what I've measured with friends before covers what I'd judge at around 15 metres (ie. not that far)... shout is six times that. So ... as an example if you're at the whompas in athen a shout may be heard to about the south side of the hill.. but no further than that.
And what's with the 3 posts after my first one giving the same info I did...? People just don't read before posting do they...