Yeah, I have to agree that's kind of wierd. Dual Cannons or Dual Beam Banks i can understand being front only, since they are supposed to concentrate fire for an Escort. But with a 180 degree arc, two Cannons front and rear should give 360 degree coverage, with NO overlap, making them different from Beam Arrays.
Then again, maybe that's the point. The only energy weapons that can be mounted in the rear are those that overlap in the broadsides. (Beam Arrays and Turrets)
I've also thought Dual Beam Banks to the rear would be interesting, especially since torpedoes have the same arc and can be mounted aft. However, for a foe on your tail you would probably want burst damage, not DPS, unless you were planning on KEEPING him there. And in such a case I can see the Escort just running to the fore or broadsides. Same problem, just in reverse.
I would have no issues on running Dual Beam Banks in the rear of my ships. I prefer the DBB over Arrays. I would love to run a setup something like this on a cruiser:
2x Single Cannon
2xSingle Cannon (or Turrets)
Kindo reminds me of the weapons layout of the base design of the Omega from Babylon 5 table top game.