Because you don't want to trap your enemy, you want to kill him, as fast as possible. In order to do that you want your shots to go exactly where you aim, especially in a high speed combat when the target is in position to be shot at for a fraction of a second and especially with such a low rate of fire as most SW starfighter weapons have.
Aircraft designers stopped putting mashineguns on wings as soon as the problem of the propereller blades getting in the way has been solved, and mashineguns have RoF several orders of magnitude higher than SW weapons.
Hi... been lurking here soaking up X-Wing news for a while, but as I'm a longtime WWII aviation enthusiast, I thought I'd chip in on this sub-discussion...
It's entirely untrue that aircraft designers stopped putting machineguns (or cannons) in wings after the propeller interference issue was resolved.
Want some examples? OK...
Republic P-47D thunderbolt (8x .50in machineguns, 4 per wing)
https://s-media-cache-ak0.pinimg.com/736x/90/0b/cb/900bcb6f4df290c41182a2db8e5ecef1.jpg
North American P-51D Mustang (6x .50in machineguns, 3 per wing)
http://m8.i.pbase.com/o4/69/661569/1/86462318.bPlPKRAC._DSC8387.jpg
Hawker Hurricane Mk. I (8x .303 machineguns, 4 per wing)
http://moore-photographs.s3-website-eu-west-1.amazonaws.com/Airshow-ww2-33.jpg
Hawker Hurricane Mk. IIc (4x 20mm cannons, 2 per wing)
http://www.warbirddepot.com/dbimages/102/102-b-1280.jpg
Supermarine Spitfire Mk. I (8x .303 machineguns, 4 per wing)
http://www.largescaleplanes.com/Photostory/RonnieMurray/1-24thSpitfire/Dcp03506.jpg
Hawker Typhoon Mk. Ib (4x 20mm cannons, 2 per wing)
Curtiss P-40E Warhawk (6x .50in machineguns, 3 per wing)
https://upload.wikimedia.org/wikipedia/commons/3/33/Curtiss_P-40E_Warhawk_2_USAF.jpg
Other variants of these aircraft carried different combinations of machineguns and/or cannons in the wings, and most versions of other famous aircraft (such as the Messerschmitt Bf109, Mitsubishi A6M series Zero Fighter, & etc. featured wing-mounted guns as well.
So the idea that aircraft designers stopped putting guns in the wings is just... wrong.
Anyhoo, back on topic: Really looking forward to Wave IX, and hoping that the ARC-170 rumor proves correct. I think it's a fantastic looking ship.
I doubt the Tie SF will be part of a combo, since I'm sure a lot of people will want to buy a number of them. Without having to buy another ship along with it every time.