Jets are starting to be introduced on the SAN-LAX route, but they are not regionals, but 737s and A319s. Ameican Eagle and United Express operate the only props, using SAAB 340s and Embraer Brasilias, respectively. I think 737 sized aircraft are starting to operate on this route because:
A. The airlines want to save their RJs for long, thin routes where they would be more economical.
B. Traffic from Europe and Asia connecting into SAN has grown so much that the route warrants these type of jets.
United Shuttle started jet service from America's Finest to LAX service a few months ago with 7 daily 737 flights. That is certainly amazing, in my mind. Northwest just recently (on June 1st or 2nd) started an A319 service from SAN to LAX solely to connect with Northwest's Flight 25 from LAX to Tokyo. NW also codeshares on American Eagle's flights to LAX.
I agree usage of props is slowly giving way to RJs, but in cases where short routes like SAN-LAX, LAX-SFO, and the "Boswash" corridor where props are (or were) actively used are going to give way to smaller narrowbodies like Md80s, 737s, and A320s because of the high passenger yields and, subsequently, the low availability of runway slots for props. However, with the introduction of stretched RJs like the CRJ700 and Embraer 170, airlines like Delta and Alaska may start to operate their own SAN-LAX routes with these aircraft.
Also, TWA operates an ONT-SAN (but not back again) service with an Md80. I hope this helps!
P.S.- Purdue Arrow, would you like to comment?