Stampin' Up! announced this today to all demonstrators (I underlined for emphasis):

Double-Mounted Stamp Sets

February 20, 2009

About
a year ago, we made the decision to start double mounting some of our
larger stamp sets. We felt this would be a good way to get stamp sets
with several pieces into a lower price range–since double mounting
would reduce the number of wood blocks needed for the set.

This has not, however, been a popular decision … Therefore, we have determined to look
for other ways to reduce our costs and bring the price of these types
of sets down. This means that with the exception of some alphabet sets
and stamp sets that are part of a kit, we will no longer be creating
double-mounted stamp sets.

What does this mean in the short term? There is one stamp set in the Occasions Mini Catalog
that is double mounted. This set was already in production
when the decision to only double mount alphabet and kit sets was made.
But this will be the last nonalphabet, nonkit set we will release as a
double-mounted stamp set.

What does this mean for the long-term? All stamp sets that have
already been created as double-mounted sets will remain double mounted
for the life of those sets. So you may continue to see these sets in
coming catalogs. However, we will not be introducing any new,
nonalphabet, nonkit sets as double-mounted stamps.