It may have to do with using the DR expansion technology. I could never quite understand that (maybe Rico can explain that), but it somehow increases the dynamic range at the expense of using higher ISO than otherwise necessary for the particular lighting condition. Just a thought.
The portraits look pretty good though. Nice new samples.
Is it possible to have ISO100 and DR400? I thought that using DR400 automatically pushes the ISO up to at least 400.
Yes, pretty much all my work on the X10 is shot in 6mp DR400 ISO100 mode. My shooting and post-processing style benefit from it greatly, and the DR performance of the new X-Trans sensor on the X20 will be the deciding factor on if I upgrade or not.
I would love to hear more about your shooting at PP style. For example, do you compose using the LCD or the viewfinder? If the former, could you see that changing with the X20? In my opinion shooting portraits as you do with so much background in focus requires great skill in regard to composition, which seems like it would be difficult with the X10's OVF.
Only when you're shooting at 12mp. At 6mp, DR400, ISO100, the X10 has a (theoretical) dynamic range of 13.3 EV.