Good idea, interesting thinking. You make a good point that indeed, Asia is without an Easyjet, Southwest type of operation and question that fact. One would think that since the since low-fare air fare is so prolific now, someone would have already started it in Asia. Perhaps there is a good reason there is no such operation.
I would begin at costs, citing the high cost of productuon in Japan and Hong Kong as an answer. Almost like the NE US in that respect. However Europe too is very expensive to do business.
Lack of secondary airports? Since Asia has seen so much infastructre development in the last 50 years or so, much of it was put into large megaprojects. Old airfields as in Europe and America do not abound. So low-cost providers will still have to pay the same landing costs, rent etc.. as the big players at large airports, HKG, KUL, SEL, etc...
Competition. There is already an extravagent number of regional airlines plying the skys in east asia. From Korean, JAL, ANA, PAL in the north to Garuda, SIA, Thai, MAS, Cathay, Silk, Dragon in the south Asia seems to have a proliferation of state-owned "flag carriers" so to speak who in their cut throat competition seem to sometimes offer discount fares becuase of excess capacity.
Asia is not completely devoid however of Low-fare, albeit not on the scale you speak of. Most are small and fly domestic routes such as Skymark in Japan or the new JAL subsidiary JEX. Philipine Airlines serves a cheap niche in that archipeligo. SilkAir I beleive keeps the fares low so as to entice pax to transit to long distance high fare SIA routes.
Its a good question however, and who knows in the next few years there could be an "AsiaJet" or something of that nature. It may even be a questioning aviation enthusiast Dartmouth grad.