My Volvo v70R has brembo calipers on the leading edge of all four rotors and I posed a similar question concerning the engineering principle behind this placement.
The most reasonable answer concerned the caliper being less debris prone in that position.
Here's the thread on
SwedeSpeed
I guess bottom line is essentially that the caliper location is almost always done for a specific reason, wether it be cooling, center of gravity lowering, debris dispersement or whatever. I don't think stopping prowess is necc effected by the placement, but some of the ancillary factors of braking can be effected by placement.
-bear