The difference of the two steering wheels while minor, are different enough to still make a difference. If you look at the center cover of the European ones it seems less bulky and more rounded at the top giving more visibility to the dash ares via the opening. I addition, it seems that you get slightly more of a grip area on the bottom half of the Euro version.
Here are better pictures, you can see the raised cover area aboved the horn seems more significant on the NA versions.
Euro version
both have the dimple leather just poor cam angle .. never had a flat bottom wheel what's the plus of it ?
I would say the flat bottom steering wheels makes it easier to get in and out of the car and leg clearance.