[CentOS] Yum: strange dependencies

Hi all,
On Centos 5.4 minimum installation, I tried to install these packages
(notice the dependencies):
===================================================================================================================
 Package                      Arch              Version
                 Repository            Size
===================================================================================================================
Installing:
 mc                           i386              1:4.6.1a-35.el5
                 base                 2.1 M
 mdadm                        i386              2.6.9-2.el5
                 base                 827 k
 ntp                          i386
4.2.2p1-9.el5.centos.2.1                updates              1.3 M
 sudo                         i386              1.6.9p17-5.el5
                 base                 218 k
Installing for dependencies:
 exim                         i386              4.63-3.el5
                 base                 1.2 M
 mysql                        i386              5.0.77-4.el5_4.1
                 updates              4.8 M
 perl                         i386              4:5.8.8-27.el5
                 base                  12 M
 perl-DBI                     i386              1.52-2.el5
                 base                 600 k
 postgresql-libs              i386              8.1.18-2.el5_4.1
                 updates              196 k

Transaction Summary
===================================================================================================================
Install      9 Package(s)
Update       0 Package(s)
Remove       0 Package(s)

Total download size: 23 M

I didn't want all those dependencies, especially exim and mysql. So,
instead of installing mc, mdadm, ntp, and sudo at the same time, I
installed them one by one and this time no exim and mysql (mc still
wanted perl, fine) dependencies. Any thought why was that? Thank you.