The internal costs were pretty much the same around the time the board was designed and having aDave, Looking this over, it *can* be routed on two layers, so using 4 would be for noise control reasons I assume?
ground plane made the decision pretty easy. Toss in the BOM cost vs the sale price and that slight
additional cost was in the noise.
Ah the good 'ol days when profits where so good. But there were times I've seen a 4 layer board where
2 would have been close to an overkill.