The coins that are known to be Satoshi's (because they were mined when Satoshi was the only one mining) can't be spent without people knowing about it. But the coins that were probably mined later, where we don't know who mined them? Those can be spent easily.

It's pretty likely a fair number of coins belong to Satoshi, as mining must have been pretty easy in the days when people paid 10,000 bitcoins for two pizzas.