Actually, American's conversion of three regional jet flights to mainline (MD-80s) is primarily due to the downsizing of the St. Louis hub. Effective November 1st, American will no longer fly from STL to CLE, which has been recently served by 5 daily MD-80s. Since American deemed this to be a "low fare" route (Thanks to Southwest), the route is being discontinued and AA is attempting to redirect CLE west-bound passengers to connect in ORD.

Aside from that, I do think it is worth noting that Cleveland's primary airline, Continental, has no mainline jets on the ORD-CLE route, while AA and UA have nine daily mainline flights between them.