The DNS CNAME (or is it A) record for
www. is pointing to your old address. The new record for your base DOMAIN.TLD is pointing to your new IP address.
If you want to get technical (and more standard) you should not be able to go to a site via DOMAIN.TLD, it should always be HOSTNAME.DOMAIN.TLD.
This behaviour is stated in the RFC for DNS I believe. The only reason people mangle their DNS record for non-host names is so stupid, non-computer savvy people can get to them even if they don't know anything.
Lets not forget that DNS changes take a while to propagate to every DNS server on the Internet, which can take 1-5 days depending on updates.