With all the enthusiasm of large crowds and outspending Hillary 3 to 1, Obama still could not close the deal in Pennsylvania -- just as he couldn't in any of the big states.
In fact Hillary seems to have won by double digits.
That's a major victory for her.
No matter how much money Obama can raise and no matter how big his crowds, superdelegates have to recognize that Hillary is the one who delivers the big states Democrats need to win in November.
Why can't Obama close the deal?
		
		
	 
I don't think anyone expected Clinton to 
not have a majority of Pennsylvania's vote. My only surprise is that she won with 10% rather than in the area of 6%. Ultimately, its a proportional distribution system, and Clinton will inch ahead by a negligible margin -- probably bagging a net gain of ten to twelve delegates. In the end, nothing changes.
Like I said earlier, its important not to make Clinton's victory in Pennsylvania into something that it isn't. Its not a decisive turn or Stalingrad-esque victory. 
She can't win the nomination at this point, unless she was pulling regularly around 70% of the vote in each remaining state -- which won't happen. Either that, or she convinces super-delegates to vote against the delegates and the popular vote -- which isn't going to happen either. And I don't like it that Clinton is hedging on that idea.
As far as why Obama can't defeat Clinton -- the same argument could be made against Clinton. Why did she fail to seal the popular vote, despite originally having all of the advantages? Why the hemorrhaging of so many states? How could she go broke so many times? How can a relative newcomer cause so much trouble for her to seal a nomination that so seemed to be hers? Why could she not close the deal? Why did it drag on for so long? 
I don't ask those questions to disparage her, but to point out that the same rationale can be used even more strongly against her.
Ultimately, the reason that the primaries are still going on is that the Democratic Party has two strong candidates. Its folly to expect either of them to "collapse" to the other, and its spin to disparage them for not being able to decisively destroy the other. Neither can, since both have their respective demographics which do well in different states.  Clinton can hang on as long as there are states that favor her demographics. 
In the long run, its over. Looking down the road, Obama has the nomination.