Also, with the exception of T-Mobile, all of the US carriers charge per device (per day) for international data - are you all really willing to pay an extra $10 a day to use your watch instead of just putting your phone in your pocket?
I'm not familiar with Non-US carriers' international data plans. I do think this is a huge bummer for European customers. Though I think anyone would only realistically travel between France, Germany & Switzerland (and maybe the UK) since those are the only supported countries at the moment so it only affects people that would do that regularly.
EDIT: T-mobile doesn't even have free 4G internationally, it is limited to 3G which the watch doesn't support - you have to buy an on-demand pass to use 4G - so any US customers that are mad about this are definitely overreacting.