The libtool RPM installs an executable called libtool, which
includes some system specific information gathered by the
configure script. This information could concievably be
different for different platforms, but the same noarch RPM
is used for all platforms.
It is true that the one package will `work' on all
platforms, but it may not be correct on all platforms.
I don't know if this bug has been fixed in 5.9
Red Hat systems are similar enough that libtool is safely a noarch
package. Red Hat also explicitly does not include the per-arch
libraries. This has been made explicit in libtool-1.3-2.