Explanation, just in case: The old hat had a story behind it (don't remember what it was, though) and held a lot of sentimental value to Ash. He spent a lot of episodes talking about how important it was and fighting to get it back anytime he'd somehow lose it. And then, from what I can tell, he went and trashed it for a new one for no reason at all.

yes the hat was the only thing which matted

they changed his hat :P