When I was your age (here comes the grandpa speech) I used to be a Metallica fan...then they released the single "Turn The Page". And I hated the song; I wouldn't even give it a chance. Now I think it's perhaps one of their best songs.
Sure, AC/DC haven't changed all that much, but they're using a timeless template for their music - blues and hard rock. The stuff's never gonna grow old; it'll always be popular. A band like Korn is only going to have a limited shelf life because they're very much of their time - much like so many "hippie" bands of the late 60's, glam and disco groups of the 70's and cock rockers of the 80's.
Nu-metal is a genre that has pretty much exhausted itself in the public eye. SOAD are one of the few bands that survived that period because they were never strictly speaking of that genre - to me they are more of a modern metal band that have changed their style just enough on each album, just as Pearl Jam have survived because they had nothing in common with Nirvana even though they were both lumped in together as "grunge" bands. Heck, even Nirvana changed their style by the end.