Do you read? The OP received a camera with only an EU cable. It is an EU camera (by definition cannot be a grey import). It seems that the UK cable was simply omitted.
As for US working, I have a 20D with a US charger, and I can use a straight converter (not voltage converting) to charge. Almost all chargers nowadays are multi voltage.
The camera itself is, obviously, identical.
I prefer the US charger. All my electronic devices either came with US plug, or have a slot-in US plug. When I travel, I use the US plug as it's more portable (swivel out vs the 3 prong brick that is the UK plug) and it's more universal.