The revision number is determined by information stored in the .svn subdirectories. Subversion will not know this is a version controlled project if they aren't there.
Usually one does not include these in a tarball and you probably did not either (does not make sense normally).
To work around the "tarball problem", Daniel made a quite smart modification to make dist which generates a distribution that does not need those directories.
However, the generated file is unluckily overwritten due to a typo in the svn version of autorevision (one == should be <=). Thus, until the updated version is in svn, the only valid way of building and having version number information is from the working copy, sorry.