forget the percentages!
here's what really happened in massachusetts

Scott Brown (R) - 1,168,107
Martha Coakley (D) - 1,058,682
Joseph Kennedy (I) - 22,237

now take a look at the same state in 2008:

Obama 1,904,097
McCain 1,108,854

in other words, brown picked up 60k votes mccain didn't get, while coakley lost nearly 850k of obama's votes. more than 3 quarters of a million obama voters stayed home.

in spite of tales of traffic jams outside polling stations, the turnout was far smaller than in 2008.

the big winner that year was john kerry, who outpolled obama as well as brown:

John Kerry (D) 1,959,843
Jeff Beatty (R) 922,727
Robert J. Underwood (L) 94,727

taking a look at the swing vote, afraid i have to use percentages after all: i heard dems are 37% of massachusetts registered voters, and polls indicated 18%, 22%, or 23% of dems voted for brown. that's bad news for the theory that the greater number of independents decided the race, because even the lowest estimate of dem crossovers more than accounts for brown's 5% winning margin, if they turned out in the same proportion as the independents. if not, the stay-at-homes decided it.