Not to mention that shoulder width also helps with the coveted 'v-taper' the chest is never gonna help with that.
Arnold was a freak with his chest, but i think the importance of a big chest has just come from Arnold having such a large chest and the importance of the Bench press has also got mixed up with that. The fact is you can bench press all you want and unless you have the genetics you will never have a chest like Arnie. Ok so shoulder width also can be determined by the length of the clavical, but IMO you can do more to change the look of you body by working the shoulders, than you can by working the chest.
I was admittedly completely ignorant to this untill GL put me right, but it really does make blindingly clear sense now.
Look at any of the 'old time' lifters and they all have impressive shoulders... Sandow, Grimek, Park, Reeves, Eger, Koszewski... some have great chests too, but ALL of them have wonderfull shoulders.