Contrary to what the rather blase rules state about implants, regardless of how "neutral" a donor organ is, there is a chance of rejection. Perfect to near-perfect matches will always be better than "mostly good" matches. This isn't listed in any rule (as in a die modifier or some such), it's more of a fluff thing. Which is, unlike wargames which require specific rules and rulings, the other half of the equation for RPG's.
I can, however, see how your statement might be the truth, as well. If specific transplants are cheaper, then they would be the choice of the multitudes of the SINless. I still don't agree, I feel it's the other way around, but I can go with it 30% or so.