-RELEASE is a snapshot of -STABLE, basically. Packages are built for -RELEASE once its out and no more. On the other hand they are rebuilt every two, three weeks for packages on -STABLE.
You don't have to use -STABLE to get packages from -STABLE version. Just set PACKAGESITE env like so:
setenv PACKAGESITE ftp://ftp.freebsd.org/pub/FreeBSD/ports/amd64/packages-9-stable/Latest/