Well, if we're talking about "millions (or more) of page views per day", as the article is, the cost of buying an extra domain for static content is insignificant. You could also serve your static content from your CDN provider's domain.
I would argue, IMO, when you need to expand you subdomains in the future, mixing naked domain and subdomains is even more uglier, and cause the inconsistencies, e.g.
example.com api.example.com admin.example.com
When we are talking about the default, it should be safe to use, and "www" is the safe choice here for people who NEVER heard about the CNAME and the cookie issues. Advertising something (like http://no-www.org) for the matter of taste without mentioning the potential drawbacks (even there are workarounds), is irresponsible IMO.
That seems perfectly normal to me. The first one is the main service, the second is the API for that service, the third the admin site for that service.
Whether you use www or not wont it will still be two DNS requests?
www.mysite.com
static.mysite.com mysite.com
mysitestatic.com