I was actually spelunking through the Angular source the other day, when I came across a comment noting that Angular avoids using closures for information hiding, due to their poor performance characteristics. Instead, they prefix private variables with a $$ prefix and leave them exposed to developers. Perhaps the Ember team made a different decision in this regard (NB: I don't mean to suggest that this is the sole reason for the difference in performance, just that these might be the kinds of decisions that matter).