Excellent observations, everybody! Here for the record is all the AT40 acts mentioned in 'Life Is a Rock (But the Radio Rolled Me)" by Reunion:
Mott the Hoople Righteous (Brothers) Harry Nilsson Brenda and the Tabulations Carly Simon Rolling Stones Johnny Cash Johnny Rivers Mungo Jerry Dr. John Leon Russell Miracles Wilson Pickett John Denver Donny Osmond J.J. Cale Z.Z. Top David Bowie Steely Dan Edgar Winter (Group) Eric Clapton
Rick Nelson's "Garden Party" contains a sly reference to John Lennon ("Yoko brought her walrus."). Stevie Wonder mentions the Jackson 5 (who happened to be singing backup with him) on his hit "You Haven't Done Nothin' ''.
Tom Tom Club's "Genius Of Love" mentions James Brown.
That song also mentions Bootsy Collins, but Collins never had a Top 40 hit billed individually, so it doesn't qualify.
The song also mentions George Clinton, Smokey Robinson, Bob Marley, Sly and Kurtis Blow. Though like Bootsy Collins, Kurtis Blow and Bob Marley never reached the top 40, and though he reached with Parliament, I don't believe George Clinton ever reached as a solo artist.