I think we've got carried away with the hypothetical value of 4x. At 4x your assessment would be blatantly true. At somewhere twixt 2x and 3x Sony's attitude makes sense when combined with that consumer mentality I pointed out a couple posts back, ie that the majority of consumers will always go for immediate savings over the long term perspective, so that if a 3x OEM MC cost $50 most consumers would shy from it and purchase only a single $20 card every 18 months (ie as needed)...and of course end up scrimping on saves with the cards they already owned rather than using 3 or 5 saves every game and having to buy another card all the time.
Though Sony may have been more off than I originally reckoned: a 4x (whatever) card would've done well to combat 3rd party cards wich were always cheaper and whose royalties must not have equated to their own MCs' profits. Sales might have been furthered by the bad press from Performance's MCs which crashed enough to make all 3rd party cards suspect--early on at least.