The comment you are responding to (mine) literally cites this answer:
"As an ISP, we often have to go to great lengths to teach users that 'www.domain.com' and 'domain.com' are two different domains"
It takes only a little bit of thought and empathy with the common user to imagine how this could be confusing. Are you supposed to type in www with every site? Why did it not work when I typed it in? Etc... It's just confusing and unnecessary.
They're not changing whether you have to type it in. They're making it look like you didn't type it in when you did. This adds to the confusion you're complaining about, as the URL bar will look the same when you type in domain.com and it works as it does when you type in www.domain.com and it doesn't work.
"As an ISP, we often have to go to great lengths to teach users that 'www.domain.com' and 'domain.com' are two different domains"
It takes only a little bit of thought and empathy with the common user to imagine how this could be confusing. Are you supposed to type in www with every site? Why did it not work when I typed it in? Etc... It's just confusing and unnecessary.