That's an interesting point.  I suppose my response would be that calling Obama an elitist doesn't mean that he's equally elitist to all other politicians, but more so than them.  Saying he's typical undercuts this argument.  

I would assume that the McCain campaign is aware of the bad (for him) generic Democrat vs. generic Republican numbers.  Thus, saying that Obama's a typical Democrat---or a generic one---seems to undercut what needs to be his argument, which is that (for whatever reason) Obama is more unsuited to the Presidency than other Democratic politicians.

Let me give a few examples:

"Rodney Harrison plays dirty.  He's a typical football player."

"Mitt Romney doesn't care about average Americans.  He's a typical businessman."  

"Karl Rove plays dirty.  He's a typical political partisan."

Each time, I think the second sentence undercuts the strong language of the first.  While the characteristic may still be true, it now merely means that it places them squarely within the typical characteristics of the profession to which they belong.

But it might be productive for people to start asking McCain if he thinks other politicians---particularly Republicans, particularly Bush---are also elitist/typical politicians.