I don't think there was every any doubt it would sell, after all Sony lead the market by a long way with the PS2 and the brand is still (despite Sony's efforts) very strong. Would the other consoles have done better with similar stock levels at launch? We'll never know. Have the competition gained siginificant ground this time around? Almost certainly. Will Sony eventually outsell their competitors with the PS3? Very likely.
It'll be more interesting to see how it does in the coming months - certainly sales aren't steller in the US from the last set of figures I saw. What happens when the PS faithful have got theirs?