Comparison of presidential election results to gubernatorial elections = apples to oranges. Doubly so with someone as individually unpopular as Corzine. Wait for 2012 pres results and we'll talk.
The 'unpopular' meme is overstated when it comes to NJ. Unpopularity has never prevented the Demcorats from winning 54-44 or so even after crap like the Torricelli switch.
If you want Presidential results, read the presidential results. Obama clearly underperformed Gore in the counties mentioned. NJ went from 8% more Democratic than the nation in 2000 (Gore 56%) to 6% more Democratic than the nation in 2004 (Kerry 53%) to 4% more Democratic than the nation (Obama 57%).
Corzine was personally more unpopular than Lautenberg ever was. Part of the reason he was selected to replace the also personally unpopular Torch. Besides, comparison of grubenatorial results to federal election results are often a shakey comparison for any state under any circumstances.
Your point about statewide PVI is noted, but building off what Brittain said don't you think that Obama's 57%/+ 4.3 (D) PVI showing--exceeded in the last century only by LBJ and FDR in 36--is more representative of the statewide ceiling for a Democratic presidential candidate than of a GOP shift?