A rollback of the Massachusetts income tax rate to 5 percent -- something voters mandated in 2000 by decisively approving Question 4 on the state ballot -- is said to be a key issue in the Bay State's campaign for governor. But that's not quite accurate. To be sure, the candidates have had plenty to say on the subject, especially since an August poll showed that a solid majority of likely Democratic voters want the tax reduced from the current 5.3 percent. The real question at the heart of the candidates' differing positions, though, is not "Should the income tax...