The 328JET does not have the range (with a full passenger load) for the 1050-mile flight from TUL to DCA, let alone the 1158-mile flight from OKC to DCA. The numbers I've seen give max range at roughly 1000 miles. Moreover, given the relatively slow cruise speed (for an RJ) of the 328JET at approximately 450 mph, the flights to DCA would be at least three-and-a-half to four hours (including a fuel stop) -- not terribly appealing on a smaller plane. And not much faster than connecting at CVG, STL, or ORD.
While Great Plains has more 328JETs coming online, they're not suitable aircraft for TUL/OKC-DCA operations given the range issue. And while the company may claim that CRJ's are coming online "soon," the fact is that it would be tough for them to start service in a timely manner (one of DOT's requirements) without the equipment on the property. Spirit lost its DCA slots because it had not restarted service after September 11. Awarding the slots to AirTran for Florida, as well as to Corporate for NC, also maintains some of the purpose of the original slot awards to Spirit for service to Florida and Midway for service to RDU (in NC). Moreover, fares to DC from OKC and TUL are already quite competitive -- comparable to MCI and ORD, and considerably lower than from IAH or DFW.
Do a quick market analysis: OKC-DCA is 1158 miles with an average one-way fare of $200 and 87 passengers each way per day (DOT's 2Q02 figures); this is an average yield of 17.3 cents/mile. ACA (which operates 328JETs and CRJ's, along with J32's and J41's) recently posted a CASM of 15.8 cents. Assuming Great Plains' costs are similar (ignoring the fact that ACA doesn't serve food), and assuming they can get the same yield, they'd need to run a 91% load factor on those flights to simply break even.