It will be costly for them to manufacture the memory chip. Easier for them to buy memory chip from established manufacturer.
And IMHO, 4x1GB cards is better than 1x4GB card. You invest more (you pay more) on 4x1GB cards, but if one card fail, you still have 3x1GB cards, while in 1x4GB card, you lost the card. Ok, lifetime warranty, but how about if you are on traveling? Precious moment captured on the card is lost... :cry: .
Since it is all about electronics, anytime card can fail without any notice.
Regards,
Arto.