(assuming they digitise books at their current rate)

Very true, but this is a snowball situation, and that current rate won’t stay at the level it is now; they’re going slowly at the moment because the legal shenanigans are still being worked out. Once they know they’re safe, they’ll throw a great deal of money and resources at it. Google are canny players, they know exactly what they’re doing – and there’s a new conglomerate trying to sideswipe with the same idea. For better or for worse, it’s not a case of ‘if’ but ‘when’, IMHO.