Well the first upper assembly ended up being smashed up a bit on the lip, but I chalked that up to the novice guy pressing it in at the LBS. They were apologetic and replaced it with a whole new assembly without questions. Second assembly went it just fine, and when I was first building it last year, the upper bearing went it fine, sure it was harder to pop out than the bottom but it was still coming out without problem.You are right it shouldn't matter at all if the headtube is within the proper tolerances for the press fit. If the headtube is much under 43.7mm like you said it will squeeze the headset cup and probably make the bearing hard to get out like Eurospek is experiencing. That's the only thing I can figure that would make the outer race of that bearing hard to remove.
Euro, How hard did the upper cup go in when you pressed in the upper assembly?
I'm thinking it's just seized up (I had a light coating of grease between cup and bearing) but next time I'm using some anti-seize paste instead. I'm thinking that the headtube can't be undersized, since the bearing was turning smooth by hand and never had problems when the fork was installed.