In most cases you aren't "stuck", you might be able to install a newer version of a package. If this can be done easily depends on the developers of that particular package.
you "can" install anything
just sometimes NOT easily
a good example is the DEVELOPMENT version of The Gimp
even on fedora the DEV version often NEEDS !!! to have installed a NEWER version of glib,glibc,packageconfig,gtk,....
now some of these are a PAIN IN THE "bleep" to have two versions of the software installed
so you CAN but it might not be easy
also you REALLY do ( most of the time) want a distro that is STABLE
RHEL6 is very stable
BUT at a cost
The versions of used programs are a bit OLD
and the "2.6.32 " version of the KERNEL