Tinstaafl,
Can you read my post again please?
You'll note that I wrote: "More than would be required for replacement of the existing fleets". In fact most of these orders seem to be for additional aircraft.
As for them being faster - No, not particularly. Carrying more PAX? Actually the trend seems to be for less passengers on regional jets.
The reason that they are attractive is due to the projected operating costs - maintenance intervals, SFC & reliability for example, being better that for the equivalent Airbus or Boeing.
However, I must add one caveat - these aircraft aren't likely to enter service for another 2-4 years.
BF.