I guess he meant "commercial English", i.e., encompassing large markets. For instance, I love Iron Maiden, but they sound very North-American. Then, in interviews, I find really hard to understand what they're saying.

Yes, it's true that some English bands sing in mid-Atlantic accents, but that's not because it's somehow impossible to sing in an English accent.

I think song lyrics are often easier to understand than ordinary speech just because they're slower, independent of accent. For example, I find it easier to understand Spanish in songs than I do when someone is speaking at a normal conversational pace.