Tyrphanax said:
Palpatine preferred quantity over quality (which is why TIE fighters don't have shields as it was cheaper to just replace a TIE than to keep one running apparently).
That's something I find very interesting about the EU in general - the different ideas people have for things. It's back to the imagination part of the equation. Plus you can take or leave whatever you want. I haven't seen the last two films, so I don't know where that shield explanation comes from (film or EU novel).
In Death Star, the TIEs don't have shield generators, hyper-drives, or emergency life support systems because those all add unnecessary weight to the craft. One of the pilots comments that because of all that, the fighters are more fragile but much faster.