The reason Zumiez sales are down are the same exact reasons most core skate shops have seen a decline in sales. A lot of the brands that were really paying the bill fell through the floor.
Core skaters have a hard time realizing/accepting this, but brands like Diamond, Obey, the Hundreds, Rook ect. really helped skate shops stay ahead in terms of dollars, sometime even keeping shops in business.
There are some really great stores out there that haven't gone down that trend road, but few of them are making bank.
If you really want your local core skate shop to stay around, really think about the fact that every dollar from every skater matters. Including you.