At Tech Ed USA I routinely meet people who have come there from Europe, Australia, Japan, and so on. This is particularly surprising for Tech Ed, because there are Tech Eds held in those places every year (usually - Tech Ed Europe is moving from Nov to July and skipping 2011, special case). At PDC I see even more - typically half the attendees are not from North America.
As a Canadian employer I have sent my staff to Tech Ed USA. I've never sent anyone across an ocean, but that's because nothing compelling has come up that far away. Plane tickets to London or Barcelona are not that much more than to Los Angeles or Orlando, so for a good conference, I wouldn't hesitate. If it never occurred to you to ask, try running the numbers.
DevConnections costs $1500 to attend without precons etc. Flights from LHR to LAS cost roughly the same (I just searched on Travelocity and got prices on real airlines.) 6 nights in a hotel at $250 a night are also the same. So by asking to be sent to Vegas you are only adding 50% to the cost of the conference. Actually, since you're being paid to attend, you need to include your salary for the week in that cost too, so it's even less of an increase than 50%. The value is probably 2 or 3 times though, because it's just FUN to be sent overseas for work. I think it's worth looking into.