I think, too, that most of the starters didn't have as much to prove this year as they did last year. In last year's spring game, Austin Collie was just off his mission, Harvey Unga was trying to fill Curtis Brown's shoes, Dennis Pitta and Andrew George were taking the place of Harline, and Max Hall was getting serious competition from Cade Cooper--they all needed the chance to prove themselves on the field. When Cooper went down on like his first play, then Brendan Gaskins got the chance to show what he could do.
This year, the starting offense is pretty much set, as are all the vets on defense. Thus, Mendenhall had the luxury of letting the 2nd string guys show what they could do in a realistic game-type scrimmage. I would expect that Mendenhall will play more first-stringers in future Blue-White games in years where the starting positions are not yet set in stone.
And yes, chalk some of this up to Mendenhall progressively improving as a coach--he now recognizes the need to keep secure starters (like JB in 2006) from going down because of fluke injuries during spring ball.