I might as well re-run the previous post on the offensive end of the ice:

 IN OUT
 GP G/GP S+G/GP SVPCT GP G/GP S+G/GP SVPCT DELTA
N=28 Better +/- 1610 1.89 21.77 913.3 686 1.71 21.16 919.1 5.8
N=25 Worse +/- 1229 1.81 21.76 916.9 821 1.81 21.32 914.9 -2.0

Again, the "Better +/-" group had a significant impact on scoring when they were in the lineup: +14.5 goals per 82 games. The "Worse" group generated more shots on goal, but scored less often, resulting in no increase in scoring.

As a whole, here are the offensive and defensive contributions in and out of the lineup:

 IN OUT
 GP G/GP S+G/GP SVPCT GP G/GP S+G/GP SVPCT DELTA
Offense/GF 2839 1.86 21.77 914.9 1507 1.77 21.25 916.8 1.9
Defense/GA 2839 1.86 21.79 914.5 1507 1.95 21.97 911.0 3.5

So we get what we expect when the players are in the lineup: the expected record of a large number of teams is .500. When a top D-man is out of the lineup, both offensive and defensive shot volume and quality suffer to varying degrees, resulting in a .450 team in the aggregate. The difference between these two teams is approximately 8.66 points in the standings, or a little more than four wins. This seems like a reasonable estimate of the value of the average #1 or #2 defenseman.

If we look purely at the change in goals allowed due to not having one good defenseman in particular in the lineup, it accounts for approximately six goals per season. The difference in expected save percentage between the best and worst defensive teams using a simple shot quality model (see: http://www.behindthenet.ca/2008/5_on_5_goalie_shot_quality.php?sort=7&mingp=20) translates to approximately 20-25 goals per 82 games. If we assume that having neither a #1 or #2 defenseman on your team costs you twelve goals on shooting percentage alone, it seems unlikely that much more than half of this 20-25 goal difference is due to a weak defensive corps.