I think what some have tried to mention is the fact that although Sampras was quite dominating in his time, he still lost to players ranked around the top 10. It's not like Federer and some of his high ranked opponents, say Roddick only beaten him once. If we consider say, Sampras and Agassi, they are 20-14 Sampas. Federer has only lost once to Roddick, who is considered one of the top ranked players in the last couple of years. Whether or not they had tougher competition, it can be said that Sampras didn't utterly dominate over almost every single top ten player that he faced, while the same cannot be said for Roger Federer. What I'm trying to say is this, from Sampras's viewpoint, he probably agree in saying that his opponents were very tough as he lost to them more than once or twice.