You can't really compare an MD with a PhD... they are both doctorate level degrees in totally different things. It's like comparing a PhD in Physics to a PhD in Social Sciences. Just because you've gone to school for a long time doesn't make you anything comparatively to someone else.
Also,
Wiki entry. It's pretty accurate as compared to what I've always believed to be the difference and what it seems others I know feel the difference is.
"Soft" sciences aren't bad and hard aren't good. But, like the link above mentions, it seems that there's a common sense application of the terms. Physics is a hard science because labs are built, lasers a fired, and things are scrutinized. Biology is a soft science because much of it is guesswork, much akin to an MD making decisions base don observation with no real "proof" of the ailment. It's why people are misdiagnosed so often. It doesn't mean biology or medicine are bad, it simply means that determining concrete proof through the scientific method is not as easy. That is, of course, changing a lot these days, primarily due to genetics moving to the forefront and labwork becoming more rigorous and tests being made available that are better able to determine the actual problem rather than guessing the problem based on several possible symptoms.