DEF is different from DPF. With the particulate filters (2008 thru about 2010), they increased the exhaust gas recirc and filtered out whatever didn't get re-burned.
DEF uses a catalytic filter and the DEF fluid to wash the particulates out. The EGR rate was reduced.
People who know and people who have owned coaches with both technologies say that DEF is a great improvement. At any rate, if you look at a graph of gas vs. DP class As, the turning point was when the government got involved.