That's the advantage of the Beatles being such a short-lived band, people tend to look at their "rosy" past. A short-lived career makes people exagerrate the band's actual greatness and talk about the could have's and would have's instead.
A big example of an extremely overrated band was Nirvana. They had the benefit of having Cobain die at the peak of his powers - thus people think of him as some great rock god. But had Cobain lived, Nirvana would surely never had been acknowledged as a great band and they would just be wherever Pearl Jam, Stone Temple Pilots, Silverchair, Soundgarden and the Black Crowes are today - just a bunch of nobodies or disbanded.
The Beatles retired at the peak of their powers, and Elvis died close to his peak. Look at other great artists from the past - their legacy is somewhat underestimated or underrated simple because they have used up their welcome and have become parodies, laughing stock and the butt of late night tv jokes --- Rolling Stones, Michael Jackson.
Had U2 died in a plane crash in 1987 or 1988, or Bono comitted suicide or U2 decided to quit at that time - they would have had a legacy of Beatle-like proportions. But U2 went on and on and reinvented their sound numerous times never to go out of fashion --- and up to this day continue to make great music that still sells to the masses. U2 have the impact of the Beatles, the swagger of Elvis, the longevity (without the parody) of the Stones -- all rolled into one while keeping their relevance.
I think U2 are a greater band than all those other bands rolled into one. It shows insecurity and inferiority when a band calls it quits at the peak of their powers - I guess they feel they can't outdo their previous efforts. The Rolling Stones stayed beyond their peak because they want to be a commemorative trip-down-memory-lane band. U2 in the meantime only record new albums if they feel it will outdo their previous efforts, and most of the time they succeed. U2 don't rest of their past successes but always bank on their newest music to drive them in tours and in promotions. U2 don't live in the past but always look forward. U2 are the best and no one compares. Enough said.
Cheers,
J