I don't entirely understand the web's obsession with 'www', but accepting it, for any given web-related DNS request I usually make a point of registering both 'sub.domain.tld' and 'www.sub.domain.tld'. But we end up manually creating CNAMES every time. To make matters worse, we have a somewhat fouled-up DNS setup (working on it!) and so we have to make DNS changes on both a Windows Domain Controller and on a Time-Warner Business Class web interface. Is it possible that there is some way we can have www.anything-in-our-domain always CNAME to its immediate parent domain? If not, will that ever be possible?
You should look into using wildcard DNS entries.