Obviously it's going to depend on the actual name and in the event of there being 2 different owners, whether a user can quickly work out they are in the wrong place (if you both do the same thing then it's obviously a problem). I think to try and get a full set of names (plurals, different extensions) of a meaningful name, nowadays, is going to be tough - and ultimately for the vast majority of businesses it's only one component of their success. So I'd say while it's nice to have all the bases covered, if the name works, I don't think it's fatal not to have all the variants.