"West Coast shuttle?" That would simply be insane. How do you compete with WN's 22 LAX-OAK flights (not to mention 14 BUR-OAK, 13 ONT-OAK, and 8 SNA-OAK, as well as AA & UA on LAX-SFO) flights when you only have 25 slots and you'd like to keep some of those for more profitable transcon service? Why pick a fight against the most profitable major carrier with the least debt and the lowest costs on routes which they dominate? Picking a fight with WN with a fare war is just bad business. Especially given that it's not clear that B6 has a cost advantage over WN on short-haul flights. While B6 does have a lower system CASM, they also have a considerably longer average stage length which lowers their CASM; that's why the financials occasionally refer to a stage-length-adjusted CASM.
I agree that the main motivation for jetBlue's LGB-OAK and LGB-LAS flights seems to be the maintenance of those LGB slots. Why else would you enter two markets that already have low fares and compete against several other carriers (at least 5 on LA-Basin-to-LAS -- AA, UA, WN, HP, N7)? If they wanted to be in the LAS-NYC market, it would make more sense from a cost perspective to fly LAS-JFK.
I wouldn't doubt that LGB is the fastest-growing U.S. airport by percentage for 2002, but that's skewed by its former status as a relaive backwater -- sort of like MHT was before WN started there. Once LGB hits its slot limit, though, you can expect passenger numbers to become relatively stagnant.