Blk Flyer - your instincts are correct.
But, Ma Delta is not getting rid of RJ's. They are allowed to increase in numbers 3 to 1 with the addition of each mainline aircraft. Delta flying will be more than 50% performed by contractors (if that is not already the case).
I guess the issue might be that the RJ's are now financed by third party operators instead of Ma Delta. Comments I've been reading elsewhere suggest that Delta is being careful and conservative with fleet purchases. (Delta's fleet is young by NorthWest standards
)
Mainline airplanes are more efficient CASM and with the limitations of traffic flow at hub airports you and I can hope the trend swings back towards mainline aircraft and we (Delta pilots and Delta Management) do not negotiate to send more flying out the door to contractors.