That plus the fact that McCain is already well acquainted with Pawlenty, who is his national campaign cochair, means his absence is probably not significant, you’re right. These meetings are, in all likelihood, for the purpose of discussing the possibility of each as a running mate.
However, I don’t think the four mentioned in this article by any means constitute “the short list.” There are other likely candidates who, like Pawlenty, have been active in McCain’s national campaign and who probably don’t need a special meeting with him.