Skins you listed are coming with standard avast! package. They will never be removed. I didn't make those skins, Martin Novak made them, and I appreciate his effort... so, telling that those skins are ugly is nothing but nonsense. I know how much time needs to be put into making skins for avast!. Maybe they are not your favorite skins, but certainly they are not ugly.
Anyway, how much memory do they take up on your HD ? Is it noticeable ? Believe me, you won't even notice they6 are there, unless you still have 4 Gb HD.
Back to default avast! skin... again, it's more than likely it's not gonna happen ever. Martin Novak is Alwil's graphic designer, so it's natural that default skin is made by him. It's wouldn't be fair to Martin if Alwil make some other guy's skin as default. Also, it's impossible, Martin probably have contract with Alwil, and that's how things goes. I made 18 additional skins, Martin also made bunch of skins, RejZor made one, and Darren made one... so I guess something for everyone. Even those which hate avast! skins, should be happy, because now, they can choose skinless interface.
Abandoning avast!, one of best antiviruses out there, just because they don't like default avast! skin, is stupid. What are they looking ? Good antivirus protection or something third ? Anyway, none of those skins in download section, whoever made them, can be characterized as ugly. None of those skins have any single bug or anything like that... so they shouldn't complain at all... they should try some other antiviruses, and then they can judge. They will not get free technical support, even for freeware version of avast!, they will certainly not get those skins, and best or worst of all, they will not get as good protection, as avast! can offer...
Cheers !