It's team chemistry, plain and simple.
Seriously, I think a big factor is Scott Rolen's influence toward professionalism. I know his history is that he gets fussy after awhile, but he seems to be exactly what the franchise needed to instill an attitude of professionalism and bringing intensity. The young core is eating it up and benefitting from that attitude.
One thing that impressed me I heard in a telecast the other night. Rolen told Welsh that when he is taking grounders in pregame warmups, he throws seeds across the diamond the same as he would in the game to properly prepare. It is that type of thing that sets the tone for how the Cincinnati Reds go about their business and it is infectious.