The parent poster is talking about DPF (Diesel Particulate Filters), which remove soot from diesel exhaust and require manual cleaning and/or the regeneration process mentioned (where the soot is essentially burnt out of the catalyst).

DEF is a fluid which is injected across a catalyst in a process called SCR (Selective Catalytic Reduction) which is designed to remove NOx from the exhaust stream. SCR (and the use of DEF therein) replaces extensive EGR (Exhaust Gas Recirculation), not the use of a DPF. Catalytic reduction instead of EGR reduces the load on the DPF and increases economy, since dirty exhaust is not being recirculated and combustion is more efficient. However, they're complimentary systems, not replacements for one another.

Yes, I own a VW TDI, I know the difference between the two. AFAIK, EGR adjusts the combustion temperature so as to avoid an overly NOx-producing lean burn. I was responding to the blanket characterization he made in this statement quoted below.

>Many equally horrible solutions to this problem are employed...Others require a separate tank of catalytic fluid that must be filled regularly. _One thing that all of the designs have in common_ (emphasis mine) is poor performance and piss-poor fuel economy. Many vehicles from multiple manufacturers have had trouble with catching on fire due to emissions control systems.