If you believe that, you know nothing about your industry. The DC9 was a regional jet back in the regulated CAB days when airlines like Southern, North Central, and Delta were subsidized to fly near empty airplanes into places like Columbus, MS, Tupelo, Greenville, and Columbus, GA. They could only make money because of subsidy. The subsidy is still alive and kicking. It is just the mainline employees subsidising outsourced flying with fee for dept. airlines. When the Subsidy ended, so did the viability of the DC9 in those markets. It appears that the industry MAYBE realizing that fee for dept. does not work either. That is why, as contracts come up you are going to see lots of them not renewed. Once one airline takes the lead of larger aircraft with less frequency the rest will follow. Smaller towns like the above have no reason for the frequency they have. No one flies DC9's except NWA and now Delta. Jetblue seems to be doing ok with a DC9 sized airplane, as is Airtran. Delta got rid of it's first fleet a long time ago. Of course, they made the mistake of selling them to Valu-Jet now Airtran.
Regional Jets are necessary and without the feed, Delta would be losing more money. I think most of us agree that there is a role for an rj, however the size of that role is the question. It has a role in off peak flying for rational extra frequency and opening new routes. Never had a problem with that. The late 90s and early 2000s saw an explosion of rjs in mgmts lust for outsourcing mainline jobs. They signed ridiculous fee for dept. contracts that not only bought all the seats, but in many cases guaranteed fuel and a 10% profit. Where do you think that money came from? Me and my fellow mainline employees in the form of paycuts and job losses. This worked well when airfares were high, not so now. This is why you are going to see a lot more rjs(35-50 seaters) parked. Now as long as the mainlines (for once, not holding my breath) do not allow further expansion of the already agreed to limits on the 76 seaters, I think you will see a rational migration of flying back to mainline with a little less frequency and larger lift. A regional jet is another tool in the box and could not be replaced with DC9's unless they wanted to lose a lot more money.