Is it some hardware feature? Or production capacity? Any ideas ?
The thing is with the Moto it's main selling point over everything else on the market is the customisation (which makes the AT&T thing a bit of an oxymoron) and I imagine it is simply a case that Moto just doesn't have the ability to offer the customisation feature outside of the USA.
Take away all the customisation and you are left with an expensive (albeit attractive) handset - but one that doesn't quite cut muster spec wise with the competition. I imagine therefore European & Global carriers would find it a hard sell to their customers, especially given it's launch window co-inciding with the likes of the Note 3 and the iPhone 5C & 5S.
Moto have said they have 'lesser' versions planned for other territories. I am betting they mean 'emerging markets' (China / Eastern Europe / India) rather than targeting low-mid range hardware to the like of Germany, France, UK etc.
So yeah - it's the 'assembled in USA' that will undoubtably be the reason why it is not going to be released in Europe.
The question I would ask is .... Is 'assembled in the USA' such a big selling point to US consumers - that they would restrict their potential market so much ? I have no doubt the fact that it is assembled in the USA (with all the extra costs therefore involved) is the prime contributor to the fact they are charging $199 on a 2 year contract and potentially $600 unlocked.