For people are wondering why they would make usable on all TIE models if it would only benefit the Defender, Bomber and maybe Punisher, it's because TIE only is easier to fit on a tiny upgrade card then "TIE Defender, TIE Bomber and TIE Punisher only".
Yeah, I really don't get the hangup people have on this.
I mean, FFG didn't need to specify 'not usable on the TIE Advanced, TIE Defender, TIE Bomber, etc' on the Targeting Computer mod. Indeed, technically you CAN put that mod on those fighters...it just doesn't do anything. You can put an Engine Upgrade on a TIE Interceptor or A-Wing, too. Again, it won't do anything. But it's still possible to do.
Having 'TIE Only' on this upgrade is perfectly consistent with other upgrades FFG has released - they are being succinct enough to provide instructions on where it's usable, without providing a huge list of fighters that it may or may not actually have any effect on.
'TIE Only' also covers their bases going forward - what if it is the much-guessed 'turn all hard turns to white' that so far only benefits the TIE Defender, TIE Bomber, and TIE Punisher...and FFG spells out TIE Defender, TIE Bomber, and TIE Punisher on the card...and then a year from now FFG releases a new TIE Fighter with some hard red turns. Either the card would have to be errata'd at that point, or it would not apply to that ship. Both options kinda silly.
'TIE Only' covers that base.