The use of www is incongruous with the idea that the text before your domain name is a subdomain. The URL format I expect is (protocol)://[credentials@][subdomain].(domain) and www breaks this.
I don't think it breaks the URL format. In your domain, you could presumably have plenty of services, one of them being a web server, handled by a machine on the "www" subdomain. In practice, the only service anyone cares about is the web and so "www." has become redundant.
I'm all for getting rid of the "www" prefix. But I'm sure someone at Google researched it and found that 1% of older consumers are scared when they don't see the magic three letters. 1% means $100M in lost revenue, so the www stays.