Do you need to know HTML to build a website?
A student recently asked, "Is it necessary to know html to build a website"?
To answer you question, YES. Absolutely you need to know html if you're going to be building a "quality" website.
Certainly with the way technology is moving in the webspace, you can get away with launching a website with little or no knowledge of html, but when you begin to grow the site and enhance its capabilities, it is almost impossible to customize the site without some knowledge. I've seen some pretty nifty "blogspot" blog websites and wordpress theme based blogs, but at some point - someone had to have knowledge to get those sites up and running. Even though you can sign up for a "free" blogger account and write blog posts, insert pictures, etc. knowing html/css will greatly increase your capabilities in growing the site.
Again - it's all about quality in the end. Otherwise you can build a site without any knowledge, but your long term possibilities are extremely limited.