I think you pretty much answered your own question. Combine that with a super smooth curve, reliability, cost and bling factor, it makes more sense.
There are turbo MR2 guys that ditch the 3SGTE in favor of Supercharged Toyota 1MZ and 3VZ V6s, they don't have the potential of a built 3SGTE, but for torque, drivability and reliability, its hard to beat. I'm guessing the same sort of reasoning went into this, even if he started with a CA18DET or SR20DET (its RHD.)