Losing Forsberg and Tanguay hasn't been too much of a big deal. We've got a great number of scorers to fill in the gap. But the Avs still haven't produced a legitimately consistent 1/2 defensive pairing, as well as a solid starting goalie. Leopold is mostly injured, while Hannan looks good but we still need to see how the season goes. Last season saw Clark picking up the slack, but he's really a number 3 defenseman.
The Avs went from allowing 198 goals in 2003-2004, to 257 goals allowed in 2006-2007. Granted, it was a different coach, but losing two of your top defensemen with no one to take their place dramatically changes a team.
Losing Patrick Roy to retirement really affected the Avalanche as well as losing Blake, Foote and Forsberg to free agency. And being forced to trade Tanguay to stay under the cap has affected them as well.