Whatever the case let's use it for the benefit of an affair.
Whenever there is a new kernel available, yum downloads it and installs. This results in a long list of old kernels when booting another OS. Fedora Core does not remove the old kernels when installing a new, but could do it manually if the long list of bootable options bothers you.
[root@fedora4core]# rpm -qa | grep kernel
[root@fedora4core]# rpm -e kernel-2.6.13-1.1526_FC4
And so on %)