[Lonesome in Massachussets]

+/-2.7% points for registered voters, and +/-4.7% for Democratic voters...

Different sample sizes. As a rule of thumb, the "margin of error" is reported as 98% divided by the square root of the sample size, implying (accurate in the first two places) that the sample was 1300 voters, 430 of whom were Democrats.

[Oldeconomybuyer]

I've often wondered why most statisticians lack a sense of humor. ;-)