MSM= Media Supporting McCain?
As an aerospace engineer I have some input into what suppliers my employer will buy parts from. My employer has strict restrictions on what hospitality I can accept from suppliers (no gourmet food, just deli stuff or pizza, and it must be consumed in the supplier's workplace during a working lunch). Going to a weekend barbeque would not be OK. Such rules are standard, and there's a good reason for them- accepting hospitality does bias the purchasing decision, even if only unconsiously.
Vendors do try to give us stuff, and we have to decline- and they wouldn't do it unless they thought it was effective. Likewise, I suspect McCain is inviting the press hoping to get a good press.
I think Cox is unrealistic about the effect of favors and socializing on human decision making.