Is there any logical reason for this? I find it lame and ridiculous.

I imagine the reason has to do with the cosmetic changes that affect vampires. I have a feeling the chargen menu doesn't play well with character faces that are completely obscured by the effects of vampirism. Maybe a PC player could test it out via the console and see if anything seems weird...

That would make sense, but it still kinda svcks. I was so looking forward to making my wood elf's appearance and hair a bit different. Oh, well. Let's try it on the werewolf. ;D