Out of curiousity, I decided to browse around and check professional sites for the Doctype coding. I thought maybe it's true that it's more professional to use a validator, and maybe professionals really are all validating. And I found this.
http://auctions.yahoo.co.jp/jp/ - No Doctype.
http://www.neopets.com/ - No Doctype.
http://www.google.com/ - No Doctype.
http://www.ebay.com/ - No Doctype.
http://www.njstar.com/ - No Doctype.
Those are some very professional, business sites that I have visited recently. And some of them are very popular.
So it seems there is a world of professionalism that doesn't revolve around having a Doctype. I'm rather encouraged by that thought, and I hope maybe some other people will start realizing that just because not everyone takes the same approach to coding as them, it doesn't mean that they're any worse at coding.