@jdaviescoates Says me, since www. tells people to expect the main brand website. naked doesn't tell them anything, eg: SaaS apps often use naked for their login, and www. for the marketing site.
Check out pretty much any big brand you can think of that ought to know, www.google.com etc.
I'm sure I read a deeper article on the whys somewhere, but I was in your shorter is better camp for a long time until I realised there were good reasons for the www. being the destination.
Cookies containment from subdomains and use of CDNs are a couple of reasons I remember off the top of my head. I'm sure there's others.