no initrd

[Piscium]

I have several Linux versions on my PC.

On one partition I have Ubuntu 10.04. On that partition I have Grub's version 
that came with Ubuntu 10.04.  
The first entry in grub.cfg (referring to a kernel on that same partition) is:

========
### BEGIN /etc/grub.d/10_linux ###
menuentry 'Ubuntu, with Linux 2.6.32-22-generic' --class ubuntu --class 
gnu-linux --class gnu --class os {
    recordfail
    insmod ext2
    set root='(hd1,2)'
    search --no-floppy --fs-uuid --set 4c32b635-ace8-4e89-9cc3-3a58c7584256
    linux    /boot/vmlinuz-2.6.32-22-generic 
root=UUID=4c32b635-ace8-4e89-9cc3-3a58c7584256 ro   quiet splash
    initrd    /boot/initrd.img-2.6.32-22-generic
}
========

I have Fedora 13. On that partition I have  Grub 1.98 that I built myself from 
upstream sources.  
The first entry in grub.cfg (referring to a kernel on that same partition) is:

========
### BEGIN /usr/local/etc/grub.d/10_linux ###
menuentry "GNU/Linux, with Linux 2.6.33.5-124.fc13.i686" --class gnu-linux 
--class gnu --class os {
        set gfxpayload=1280x1024x32
        insmod ext2
        set root='(hd1,11)'
        search --no-floppy --fs-uuid --set e01eba0e-9f82-4428-aa91-ec8cec4e4d73
        echo    Loading Linux 2.6.33.5-124.fc13.i686 ...
        linux   /boot/vmlinuz-2.6.33.5-124.fc13.i686 root=/dev/sdb11 ro 
rootfstype=ext4 quiet rhgb
}
========

Note that for Fedora there is no line equivalent to "initrd ..." in Ubuntu. 
In the Fedora boot directory I do have the file 
initramfs-2.6.33.5-124.fc13.i686.img

Fedora works fine, just like Ubuntu. so my question is the following: 
is initrd (or equivalent) needed to boot with recent kernels? 

I have Scientific Linux 5.5 on another partition (which has an old kernel) and 
it did not boot without the initrd line.