What you have to realize is that people like Buffet generally don't go out and buy their entire position all at once. They often do what many other investors do - buy in the dips. In other words, they wait for drops as strategic opportunities to add to their positions, trying (when possible) to use dollar cost averaging. Buffett only has to reveal his trades when he acquires a certain percentage of a company's outstanding shares (5% I think?) because the SEC requires it. Otherwise you're going to read about it when he releases his own news or submits required filings that let you figure out what he's in.
Most of the time, by the time anyone really knows what someone like him is buying into, the market has already accounted for his trades by way of rising share prices when he buys and lower prices when he sells.
By the way, if you can figure out how to buy the same stocks as Buffet at the same price or less then that would really be something. He pays people an awful lot of money to figure that out for him now.