Although not necessary, having your own virtual domain can be worth its weight in gold.
Many search engines require that pages submitted for indexing have their own domain.
And further, some are beginning to accept only top level indexing request. This means you need your own domain name. This makes sense, with all the domains being registered, it is only a matter of time that all engines will require a unique domain. If you change service providers or hosting services, your domain name will stay the same and you can carry it with you.