Personally I don't really understand why some get so upset about this? As much as the UK has influenced other english speaking countries musically, the musical influence from the USA has been even greater (IMO).
The vast majority of people in the last 50 years-ish have "learned" to sing from USA based singers and performers, or from those who have been influenced by USA based performers. Let's be frank, The Beatles didn't exactly sound like scouse scallys did they?
If you meet (for example) a Japanese person who learned english from an Aussie or a Canadian they inevitably have the accent "fingerprint" of their teacher, formally or informally taught.
I personally see no difference in the above and some of the devotees of Trad English Folk adopting the patented working class, countrified nasal twang regardless of their regional/class origins.
I suspect that is because they learned to sing in that way from other singers that they admire/respect.
And let's be honest, some accents are just not that "musical" are they?