Casues for the 335d premature carbon build up and/or soot
From the pattern I have observed and the reseach I have done:
BMW released the letter regarding the redesigned EGR emissions sytem on May 2012
Any 335d that either racked up significat miles (~40k+) or mostly city driving (~20k+) before this update (SIB 18-02-12) they are a potential victim of carbon build up (or maybe excessive amounts of soot). The excessive carbon and/or soot need to be cleaned from the cylinder head and intake manifold regardless of the update. Only then, this updated system should prevent this issue from reoccuring.
Any 335d that received this updated system while their miles were still low may just be OK. They may only have minimal carbon build up or sooth build up (not enough to trigger the SES).
Now there are no reported cases (on the internet) where after the new EGR system update a healthy 335d (no carbon build up) is diagnosed with "new or more" carbon build up or excessive soot.
So, I wouldn't blame the driving style, but more so of the original emissions system design in the M57 by BMW.
Also the reason we don't see this issue so frequently is because not too many drivers racked up ~40k+ miles in 2 years before the emissions system update.