27512 pinout and PCB layout
Perhaps the answer is simply historical carry over maintaining pin compatability (originally going back to the '08' chip - 1K ROM).
Compare the pinout with is its much older cousin the 2716 (EPROM) - a 24 pin chip. In the 'good old days' this was the basis for developing a lot of the earlier microcomputers.

When more address lines were needed (A11 - A15) they fitted them into the extra pins. Pin 28 was designated for power so the original pin 24 (now = pin 26) was available to connect an extra address line (A13) leaving A8 and A9  and A10 in their original positions. Vpp (programming voltage on old pin 21 was not required) so this became A11 (new pin 23). This left new pins 1,2 and 27 to assign to A15, A12 and A14.
This effectively allowed older 24 ROMS and EPROMS (and RAM chips such as the 6116) to be plugged into the later (28 pin) designs.

As regards PCB traces (I'm assuming your using at least double sided) there is no problem with the order. You are simply connecting pin 1 to pin 1, pin 2 to pin 2 etc. by taking the (horizontal) trace between pins, remembering you have both sides of the board to play with. If you require the address bus in a particular 'order' bring out the horizontal traces from the memory block and use vias and perpendicular traces to re-order them.