You are right on this one. A contractor friend pointed out that if you use a larger ledger the compression on the drywall is going to be much less of a factor. In addition he says that he finds lag bolts much preferable to nailing due to the fact that the withdrawal value on lag bolts is much higher than nails and has found most failure linked to that.
He suggested a couple of over-building techniques. First, use a large ledger with multiple lag screws. Drill pilot holes for the lags through the ledger into the stud (says anyt lag over 1/4" needs a pilot hole. Then, use the pilot hole to bore a 1" or so hole through the drywall. Insert washers flushwith the drywall, bore the ledger and install the lag screws.
Secondly, he said if one is really concerned to lag bolt 2x4 flat against the wall to the floor to support the ledger.
Oddly enough I found that the lateral load value on a 5/16" lag screw is not appreciably less than a 1/2" lag bolt (220 vs 290 for 4" lag penetration in main member).
Thanks,
Jim