The European system is different than that in the US domestic one. Here are the reasons as I see them:

(1) Domestic US - no customs or INS. Europe, more flights tend to be international in nature thus requiring INS and customs.

(2) In Europe everyonegoes to a common check-in area to recieve a boarding pass before security. In the US you can check in right at the gate.

(3) In Europe, you typically go to a departure lounge (after check-in) before being assigned a gate. In the US, you can go directly to a gate.

I like the US system better. It is annoying to have to check-in before passing security. If the lines are long, I can bypass the ticket counters and then check-in at several other places ... lounge, my gate, other gate, customer service desk, etc...