touchdown17
It might matter to you (i.e. if you would rather do some flying in the States than in soggy Oxford or at FTE in Jerez). It probably won't matter so much to potential employers, unless they have a regualr agreement for supply from a training school. I don't think there's anything formally arranged with Oxford, so it would be pot luck (there may be a few such agreements scattered around that I'm not aware of, but none that are really definite and regular, excluding CTC). Pot luck and personal contacts will have a greater influence on your chances of getting a first flying job than where you did your training.
AD
Edit to say: An ATPL is only an ATPL if it's recognised in the country you want to work in. Commercial licences in the US are FAA-constructed and issued, whereas the JAA architect and issue the appropriate licence for work in JAA member states (e.g. Europe). You need to do a conversion course if you don't have the right licence for the company you want to fly for. Someone will probably help you out on the various specifics.