Is a 115V rated transformer expected to accept US mains voltage (120V)?
Up until couple years ago in Netherland (and many other EU countries) we used to have 220V(AC), others used 230 or 240V(AC). One of the good things that was brought by EU is the unification of mains power. Over several years the mains voltages have been slowly changed to 230V (+/- 10%) across mainland EU (not sure about UK). Thus a substantial part of the world is now at 230 or 120V.

Many electronic devices don't mind too much about that increase by less than 5% and incandescent light bulbs have a somewhat reduced life time but are cheap. 

Not sure what countries use 240V(AC), but do realize you are talking about a less than 5% error which is within mains power tolerance.