the http:// and http://www. "options" are "provided" by the hosting company.
I don't know why they don't do that by default.
the last option is ... to change hosts
This is not correct. Not all hosting companies support Wildcard Sub-Domains. When you use a Sub-Domain, generally, its "something.domain.com". Not many websites, let alone hosting companies use the "www" prefix at the start of Sub-Domains.