I get a -$12.25M change comparing rosters from 2011 ($112.7M) to 2012 ($100.3M) when I do the math.
-$40.4M for players on 2011 MLB payroll not on 2012: (Nathan, Cuddyer, Delmon Young, Kubel, Thome, Slowey, Repko, Mijares, Dusty Hughes, Tolbert, Manship)
-$3.65M for smaller salaries from 2011 to 2012 (Morneau $15M to $14M, Capps $7.15M to $4.5M)
+$8.5M for larger salaries from 2011 to 2012 (Span, Blackburn, Liriano, Baker, Perkins, Casilla, Pavano, Valencia, Duensing)
+$23.3M for players on 2012 MLB payroll not on 2011 (Willingham, Doumit, Marquis, Carrol, Zumaya, Burton, Burroughs, Revere, Burnett, Slama, Luke Hughes, Plouffe, Maloney, Clete Thomas, Hendriks, Parmelee, Waldrop)
That's $44.05M removed from the payroll from last year and $31.8M added for a net change of -$12.25M
Another way to look at is - there are 14 carryover players from 2011 making $77.1M this year as opposed to $72.3M last year. In 2011, the rest of the roster (since jettisoned) cost $40.4M. Their replacements this year cost $23.2M.