[CentOS] How can binaries be different when package versions are identical? (mkfs.ext3 on CentOS 5.4)

I read up on "prelink" as suggested; and used "ldd /sbin/mkfs.ext3" to
see what the dependencies (libraries) are.

There are 13 dependencies; file size is the same between servers but
md5sum's are different!

Most of these libraries have other libraries they call; I finally drilled down
to ld-2.5.so which is statically built.

Same thing: same file size, same datestamp, same package version; but
the binary is actually different; yet rpm -V does not complain.  Why?

(Both systems are running CentOS 5.4; one was deployed in December 2009,
the other in April 2010.)

[root at server1 /lib64]# ls -l ld-2.5.so
-rwxr-xr-x 1 root root 139416 Sep  2  2009 ld-2.5.so
[root at server1 /lib64]# md5sum ld-2.5.so
ad38c69452b3990852c0d3e0ea51a31b  ld-2.5.so
[root at server1 /lib64]# ldd ld-2.5.so
        statically linked
[root at server1 /lib64]# rpm -q -f /lib64/ld-2.5.so
glibc-2.5-42
[root at server1 /lib64]# rpm -V glibc
[root at server1 /lib64]#


[root at server2 /lib64]# ls -l ld-2.5.so
-rwxr-xr-x 1 root root 139416 Sep  2  2009 ld-2.5.so
[root at server2 /lib64]# md5sum ld-2.5.so
ddb5ad336c3cf40ee2c69b91ef7bfd04  ld-2.5.so
[root at server2 /lib64]# ldd ld-2.5.so
        statically linked
[root at server2 /lib64]#
[root at server2 /lib64]# rpm -q -f /lib64/ld-2.5.so
glibc-2.5-42
[root at server2 /lib64]# rpm -V glibc-2.5-42
[root at server2 /lib64]#