I wear Uggs all winter long and agree they would be awful to walk in the parks in. They are very wide so no one's foot is securely snug in them, which causes them to flop around or the person to "shuffle" in them. If I'm walking fast in them, I feel like I have to scrunch my toes to keep them from flopping around. Not comfy!
Some useless info on Uggs: they were invented in Australia for surfers to put on after immediately getting out of the water. Their fur lining absorbed sand and wicked moisture. This is why they are not waterproof or great for winter wear, even though that's how everyone primarily wears them now. So they were actually invented for warm climates