Correct, it doesn't scan files before they are opened, check HTML for malicious .js, check incoming and outgoing mail, or instant messages or anything else. I don't like software that insists on becoming part of everything else unless it is asked to. ClamWin is a scanning tool, and that's about it.

I have a powerful computer and can afford to use realtime protection, but I believe an opensource AV like Clam will dominate in the future.