Why is it that Tiger Woods is always being challenged?

No matter what place Tiger Woods may be in during any given tournament, why are the other golfers challenging him? Why isin't Tiger the challenger? Is this because the announcers have to justify the statement that he is as great as Jack Nicklaus? Maybe I'm naive, but shouldn't we wait till the end of an athletes career to compare him to another in history? I'm watching the U.S. Open and after submitting this, turning the sound down!