Build-Depends listed as a should not a must?

["Jamin W. Collins" <jcollins@asgardsrealm.net>]

Section 2.4.2 of the Debian Policy indicates that listing Build-Depends
in a source package is only a "should", not a mandatory requirement:

   Source packages should specify which binary packages they require to
   be installed or not to be installed in order to build correctly. For
   example, if building a package requires a certain compiler, then the
   compiler should be specified as a build-time dependency.

Wouldn't this be better as "must"?  Are Build-Depends really to be
considered optional?  I realize that if Build-Depends /are/ listed, it
is a "must" that they be complete:

   If build-time dependencies are specified, it must be possible to
   build the package and produce working binaries on a system with only
   essential and build-essential packages installed and also those
   required to satisfy the build-time relationships

However, "should" is classified by the Policy as:

   Non-conformance with guidelines denoted by should (or recommended)
   will generally be considered a bug, but will not necessarily render a
   package unsuitable for distribution.

This means in theory that a developer could opt not to list
Build-Depends and this would be acceptable, right?

-- 
Jamin W. Collins