Heavy Metal is a form of rock
There are a lot of sub forms of music under the rock umbrella, but the all the music discussed above is rock music, there is Heavy Metal, NWOBHM (New Wave Of British Heavy Metal - eg Iron Maiden), Heavy Rock - eg Led Zep, I would also class AC/DC as Heavy Rock.
They all appeal to the same people, few Maiden fans would hate a good AC/DC track and vice versa.
You have your favourites, but you generally don't hate other similar music types.
I remember the NWOBHM years very well, and you did not class it as different to the older bands or the more melodic heavy rock bands, it was all good music - better than the New Romantic waffle* which got the most press.
* Excepting some Duran Duran as they were actually rock musicians - remember Powerhouse?
Yes there was a split to some more extreme metal music types (eg Death Metal), but we don't talk much about them.
So basically we al listened to music played to a high standard, based on lead electric guitar, electric base, a singer with a decent range, and all displaying good musicianship.
I think Rock in the 70s and 80s was where the talented musicians went.