No, thats just how the weapons were laid out.
The weapon layout is actualy fairly good. They're able to focus nearly all their firepower to the front of the ship, and a fair amount to port and starboard. The only realy weak area is the back.
72 TIEs is crap. The venator carried over 200 fighter craft.
True, but the ISD is more designed as a warship than a carrier.
The lower hull had its sheild generator to the fore of the main reactor bulb and the upper hull had it sitting between to rows of turbolasers. Both making for very loving targets and neither well protected against fighters.
Well, the fighters would have to get through the shields first (nigh on impossible for fighters, not including the EU stupidity), then through the fairly tough armour. Aproaches to both generators would also be covered by fire-arcs of multiple guns, also.
Out of curiosity, where did you hear that the generators were placed there?
"You've all been selected for this mission because you each have a special skill. Professor Hawking, John Leslie, Phil Neville, the Wu-Tang Clan, Usher, the Sugar Puffs Monster and Daniel Day-Lewis! Welcome to Operation MindFuck!"