I wonder how much difference there is in the way that rock vocals are taught compared to how pop vocals are.
Sometimes the line between pop and rock can get blurry. The Eagles had plenty of songs that must have appealed to a pop audience...and a country audience. Life In The Fast Lane is one of their few songs that doesn't sound country or pop; it is definitively rock.
Overall, they appealed to fans beyond a strictly rock audience. Look at the album sales they did in the mid-70s. Their Greatest Hits (1971-1975) is still the best selling album in the U.S. after all these years. It is certified 38 x Platinum. That mark may never be broken. Towards the end of that same year, they just happened to release Hotel California. Talk about a good year for a rock band!
The only reason Hotel California didn't win the Grammy for record of the year is that it was up against Fleetwood Mac's Rumours album. It has sold over 40 million copies by appealing to a very mainstream audience and being a tremendous piece of art. It was one of those few times when an album's critical acclaim and it's commercial success both got as good as it gets. Fleetwood Mac blurred the line between genres just as well as The Eagles did.
More recently, on the pop side of things, Miley Cyrus has become known for doing some amazing covers of songs that venture well outside of pop. She's considered a pop star but her raspy voice and audacious stage presence fit rock music extremely well. I happen to think Miley is actually better suited for rock than pop!
All this makes me wonder: Is there that much of a difference between taking lessons for rock vocals and taking lessons for pop vocals? For a rock vocalist who has the rock music fundamentals down, would transitioning into pop present vocal challenges their rock background hadn't prepared them for?
Just as a hypothetical example, since George Michael is widely considered one of the greatest pop vocalists there has been, what kinds of things would a hard rock or metal vocalist have to prepare for to venture outside of their comfort zone and make the kind of album that George Michael might have made?
Are there actual pop techniques that Michael used that don't get used in rock that are hard to learn?
What would be the biggest vocal challenges for the hard rock or metal vocalist looking to make that pop type album?
If I had to guess, the biggest difference or challenge would probably not be an actual technique that pop requires that rock vocals don't prepare you for, but the vocal agility that Michael had, control over his vibrato and the ability to make every note sound beautiful - those seem like they'd be the biggest challenge for a vocalist coming from a style where making every note sound beautiful often isn't as big a priority as exuding a rock 'n' roll attitude with aggressiveness, grit and swagger.