I think the big question is... how would the Cowboys be most successful? With Julius as a Barry Sanders-style back, or an Emmitt-style back?
Last year he seemed to be a Barry-like back, not in terms of eye-popping jukes necessarily, but in terms of high-risk/high-reward style running... he had a bunch of big gains, but also had a LOT of negative runs.
This year he's clearly more of a "sure-thing" runner. I don't think the 3.5 average will last the whole season, and he WILL have his share of big games. But he seems to be more Emmitt-like in his approach... as in, he'd rather get a sure 5 yards than risk a -2 yard run to try and bounce it outside for 15+ yards.
And now that I really think about it, this could also have more to do with Parcells' confidence in the passing game, and more specifically Drew Bledsoe. Last year when Julius came back, he WAS our threat on offense. So his "risky" style of running was necessary for our offense to have any kind of explosiveness. So far this year, with the way Bledsoe has been playing, Parcells may be thinking that it would be smarter to make sure to get the sure yards to set up the pass.