You're quite right. It's not a fair definition of atheism or agnosticism. But enough people fall into those camps (materialist atheist vs. wishy-washy non-commital agnostics). Given those two false perceptions, I'd rather be deemed wishy-washy than dogmatic, I guess. I'll happily take the time to explain that I don't believe in God, but I don't want to try to convince them that I'm open-minded. Somehow I feel that's harder when you say you're an atheist.