I found quite some discussion over weapons and damage codes to be changed in SR4, yet nothing concerning the way how armor will be approached.

Now I found myself arguing with Cochise about whether the strictly abstract and wholesome rules of the BBB or the somewhat more differentiating rules of cyberlimb armor (relevant armor value is the average total of distributed points) and chemtech (impact armor only on targeted body portions applies) should prevail.

Because the current situation is, well, too mixed up, if you asked me.

Look at vests with plates. They protect only the torso.
Then look at FFBA III. They protect the whole body, including hands, feet and head.
Yet both have a ballistic armor value of 4.

When I shoot at targets protected by either armor without specifically aiming at a certain portion of the target's body, there is no difference. When I aim at the torso's center, there should be. The vest with plates concentrates right there, and should therefore be stronger and more resistent than the spread-out FFBA III. Difference between FFBA I (Ballistic value of 2 with the same coverage as the vest with plates) and III is the extra protection of extremities, not the thickness of material, from my point of view. When thinking along the cyberlimb armor rules, this makes perfectly sense: Overall armor is the average total of distributed points.

Take the vest with plates and a lined coat and have the target be attacked chemically. Both halved impact value equal 1 (rounded down) so an unaimed attack would be the same against either armor. Yet, if the assaillant aims at the extremities (sans head) the wearer of the vest with plates is at a loss, while the guy in the coat has the chemical's power reduced normally.

Now back to the BBB. SR3, p. 114, does not allow called shots to circumvent armor as do the chemtech rules or cyberlimb armor rules (the faq does, yet without reference to official rules.)

My question being, how does SR4 deals with this discrepancy?

I would expect a vest with plates to be much better at protecting the torso than a kevlar catsuit, even if your arms are bare. I can accept that they have roughly the same armor ratings. I place my vote on abstract. Maybe called shots reducing armor but requiring more sucesses to stage?

I do feel that the way chemical delivery works needs to be revised a bit though.

Since the object is to streamline the rules, I would hope the existing system gets replaced with something streamlined. I don't mind the basic concept of the current system, but would prefer it either go one way or the other. My vote would be for a more abstract system, which tends to help speed up combat.