Hmm, JIRA lost a comment I made on this issue before resolving (or I screwed up by editing the issue before submitting a comment I was making) - it was something like:
I confused releasing and enabling 'the maven build', which involves putting the POMs in place via ant get-maven-poms and installing non-mavenized dependencies into the user's local maven repository via mvn -P bootstrap install. The source of the non-mavenized dependencies was the lib/ directories, which are empty until ivy resolve is done, so ivy resolve is a prerequisite.
However, since there are no longer any non-mavenized dependencies (see
SOLR-3308, LUCENE-3930, and SOLR-3310 - thanks Robert Muir and Chris Male), ivy resolve is no longer a prerequisite for running 'the maven build'. I'll resolve this issue as Invalid.