There are not 10 Democratic Senators vulnerable in 2012, no matter what. Presidential years are generally neutral unless the Presidential race is an extreme landslide.
Like 2000?
+4 is within the margin for neutral, and the Republicans even gained a seat. It certainly wasn't even close to +10. But, of course, 2000 may be comparable to 2012 - six years after a large victory - which would indicate slight Republican gains of around 2-4 seats at most (especially given that 2012 will happen with an incumbent, probably Democratic, president, while 2000 happened with no incumbent running).