If I were publishing Rolling Stone, I'd do the same thing they're doing.
They're a MUSIC MAGAZINE...their target audience is going to be young-ish and liberal, so attacking McCain makes perfect sense since their readership likely going to be pro-Obama.
Thing like that cover article sell magazines, and in the end, that's what it's all about to them.
BTW, I stopped reading Rolling Stone and Spin in the late 90's when I discovered I could get more and better information on the Internet (which also holds true for most magazines nowadays).