Whatsamatter, olivant...can't handle anyone disputing your 'theories'? I'm not surprised to find out you would own such a book.
Regarding the infamous line...I've heard it discussed for more years than I've been on the BB and by bigger GF officianados than myself. The general concensus is that it is a FLAW, because no matter what its logic cannot be explained...and I happen to agree with that.
So, think up whatever Rosato Bros. 'trait', whatever 'subplot' you like...the line is a flaw, has always been a flaw, and always will be a flaw.
Luckily, while an obvious one, it is far to minute a flaw to have a lasting negative effect on an otherwise flawless movie (except for the question of who opened the curtains, who killed the hitmen and exactly how did Fredo help Roth).
Apple