Gen. Posting Groups do not flow to G/L on Inv/COGS entries

Does anybody know why the Gen. Bus. Posting Group and Gen. Prod. Posting Group do not flow through to the G/L on the INV and COGS entries of a sales invoice?

Suppose a sale (cost $10, unit price $20) that produces the following entries in the G/L:

-$10 Inventory
+$10 COGS
+$20 A/R
-$20 Revenue

only on the revenue g/l entry do the posting groups flow through to the G/L. But it would be nice if the Inventory and COGS entries showed the Gen. Posting Groups (the COGS entry especially) as you could use the G/L to get a quick gross margin by Gen. Bus. Posting Group or by Gen. Prod. Posting Group.

Anybody know why these fields don't flow through? would it be a bad idea to customize to make them flow? The place to do it, I believe, is codeunit 5802 (PostInvtPostBuf). The GlobalInvtPostBuf has the Posting Groups, but then the code neglects to pass the Posting Groups when it creates the Inventory and COGS GenJnlLines.

Thanks.