Hi guys,
I write in order to give some information maybe useful. I guess many of you have the iphone volume lower then Iphone 4S volume cos IT IS lower. You can even check it even on wikipedia: http://en.wikipedia.org/wiki/IPhone_5 (look in the "deisgn" paragraph).
I realised this 12% less can result in 2 step less in the volume bar, for instance I used to keep my iphone4 bar at 1 step less then the middle and now I have to keep my Iphone5 at 1 step more then the middle. When I purchased my Iphone5 (in Italy too) I thought it may have a volume issue, comparing it with the 4. Then I checked on internet to realise what I wrote above: the 5 is simply thinner, lighet .. and LOWER then its predecessor.
Last thing: some app like Viber, Tango, for Phone or similars may put the music volume lower, or at least it happened on my Iphone 4. What you have to do in this case is simply to double click on the cetral button (home) of your iphone and close the above mentioned app. The volume should return higher.
Should any of you have another kind of issue, your device is probably to be replaced.
Hope I gave some help