That's the thing many people need to get clarification on. It's not sure if Apple's speaking about purchasing or activating a device in the given country. This has absolutely nothing to do with roaming as that won't be possible for the launch at all. This is purchasing a device in one country and activating in another with same LTE bands.
Exactly. The issue here is that we're working from very little concrete information. Especially as we are basing this on a paragraph from US Apple support, that could be explained away with the issue of bands:
""If you purchased one (an Apple Watch S3 GPS + Cellular) through the US Apple Online Store,
it'll only work for the 4 US carriers. It wouldn't work internationally unfortunately. I'm not entirely sure what type of error it would show
if you took a US Watch to Germany, but it wouldn't be compatible with Telekom"."
"it'll only work for the 4 US carriers"
-> Of course, because the are the only ones to support the Apple Watch in the US. And traditional roaming is not available.
"it wouldn't work internationally unfortunately"
-> Again, because traditional international roaming isn't supported by carriers/Apple Watch
"if you took a US Watch to Germany, but it wouldn't be compatible with Telekom"
-> So this is both explainable by the fact that there is no traditional roaming support
AND the fact that a US Apple Watch doesn't have the UTMS/LTE bands that are used in Europe.
So quite frankly, I can't see how we have reached the conclusion that you can't EVER use a cellular Apple Watch 3 outside it's original country of purchase or usage (in a non-roaming situation).
This is the same as back when some iPhones couldn't operate from one region to another; you could as easily have said for those: "if you took a US iPhone to China [...] it wouldn't be compatible with China Telecom". That doesn't mean say, the same UK iPhone with region limited bands couldn't have been used in France.
I personally believe (wishfully) that this is just the same thing for the Apple Watch 3, and we have just had slight amnesia in our interoperable world of iPhones today. It's just the logical conclusion really; and yes it's annoying for those who want to move between regions, or eventually traditionally roam between them (when it's supported of course).
But I think we've just take too much poetic licence when we have made the HUGE STRIDE in logic deduction based on this one tiny paragraph.