Different people different experiences.
I wouldn't think that it is the North America vs Europe element. More likely just the natures of the individuals involved. My group of friends may have aptitudes that yours lack and vice versa. It could even be something as simple as having someone in each group with a particular aptitude for one system or the other to assist the others in "getting it". One thing that just occured to me. My friends pretty much all like "resource games" like Civilization, Master of Orion etc. shoot em ups are liked much less. It could be that resource orientation works well with 3rd Ed.
Yes my niece is quite bright.

That isn't just the uncle talking it is her marks. She did have the advantage of growing up in a gaming household and starting with games at an early age. She wants to join the campaign if it gets going again just to kill the halfling trader the players ran into last time. She wasn't playing and still found him too irritating to live. I modelled him on the Mr Hainey character from Green Acres. I bought the DVDs just to get the character right. I think it worked.

Obviously I also have fun with the roleplaying side as DM.
My self I prefer the roleplaying side. I always try to give my character some type of disadvantage. Some times the character gives it to himself (Dex 4 1st edition Cleric).
A 2nd edition fire elementalist who was terrified of contact with water (made the sea voyage interesting

).
A 2nd edition dwarf fighter/psion who had just come out of thousands of years of suspended animation (needed DMs consent of course) and knew no modern languages. The other players had a lot of trouble communicating with him and even more figuring out his class. He kept doing things a fighter couldn't do.

He would have told them if they asked (using the right magic to talk to him of course) as he was LG and had no clear reason not to tell them.
A 1st edition character that had some trouble with dying. Elf thief/mu(LN) - Gnome ft/th(CG) - Elf ftr/th (CN). Then wished back to life instead of reincarnated. Wished back with all the memories abilities and physical form of the 1st identity. But the personality of the 3rd. A CN with all the memories of the LN and the gender got reversed along the line. Became rather unbalanced.
1st edition th/mu (complex history) ended up with the sword Black Razor from White Plume mountain. The way I played it was that the more the character was boosted in HPs and to hit the more irrational and enthusiastic for combat it became. The character was normally played as a calm rational deep thinker. The other characters wouldn't let me use the sword except when they called on my character to use it. They were afraid if my character were boosted to far that the ability to discern friend or foe would be lost. The aggressions and irrational behaviour isn't part of the sword I just thought it would be fun to play it that way.. but only the DM and I knew that.

I haven't actually played 3rd edition only DM'ed it.
I never tried Hackmaster but had some fun with Marvel Super Heros.