I picked 4E, but it was really only the closest to what I'd like, and I think the "achievement" or whatever it s they call it when you fight two battles in a row is an incredibly stupid and arbitrary concept.
To me, an action point is a metagame concept, so why not just say "one per session" or somesuch?
Personally, I think 'One per session' would be far more 'stupid and arbitrary'. What if your session is an 8 or 12 hour, once a month marathon, and my group plays 3 hour games once a week? What if we both played sessions of equal length, but my group took more breaks, did more non-encounter RPing, etc, while yours favored a pure dungeon crawl with lots and lots of action?
A session is much more open than an encounter. I can see playing with the frequency of encounters per action point, or going to a per-session basis for an individual group, but having a rule based on X Resources/Session would have been pretty bad. As a general rule to include in a core rulebook, I much prefer what they've got than a session-based system.