The best thing about the annual Grammy nominations and awards shows is the clamor of anger that rises up when the mere mention of the event even comes up. Immediately people begin calling it a travesty, trotting out all the people who have been snubbed -- Jethro Tull beats Metallica -- plus everyone from Neil Young to Chuck Berry.
As USA Today noted today, before 1979, there were no "rock" categories at the awards, as the industry was still trying to come to grips with long hairs and loud guitars, even nearly 25 years since it went worldwide. So from say 1956 to 1979, they missed out on Jimi Hendrix, Led Zeppelin The Beatles, The Who, Janis Joplin, the list goes on.
Though I can argue at length that these folks were making pop records with precious melodies and feeling that were begging for recognition. A lot of these bands would end up with lifetime achievement awards to pacify fans. Plus, it's not as if winning a Grammy has any bearing on an artist's influence or historical significance.