For what it's worth, Mike and I ran into a Clinton insider last night who offered an additional twist on this argument: Not only does Clinton do better among registered Democrats than she does among independents and Republicans. But he thought registered Democrats would be especially inclined to give her a second look after Iowa and New Hampshire because they'd resent having their nominee chosen by a bunch of interlopers.
He then goes on to explain why this will be a tricky argument to make (it's subtle, it concedes Obama's electability argument, etc.) and then adds:
Having said that, maybe partisan Democrats really will resent the "meddling" of independents and Republicans in their primaries--and maybe they'll perceive that meddling to be the reason for Obama's success even though it's not true. (The media narrative will probably help Hillary on that front--I suspect we're going to hear a lot about independents immediately after New Hampshire.) So I'd be reluctant to dismiss the strategy out of hand.
What first came to mind when I read this was George W. Bush's eventual defeat of John McCain in the 2000 primaries, where there certainly was resentment that an influx of independents gave McCain a victory in early states. Still, there seems to be at least one crucial difference between this example and Hillary's current predicament: The GOP base already had good reason to dislike McCain. A large part of McCain's popularity with independents rested on his willingness to buck the Republican establishment and take positions more in line with the overall electorate. Obama's appeal to independents relies on other things entirely--namely his call for "change" and appealing personality (McCain also had an appealing personality, to be sure). In short, the Democratic base has no reason to dislike Obama, and thus it's hard to believe they will resent his broad appeal.