There was a known production issue with early devices that were manufactured. RIM supposedly fixed the production issue, but there were still thousands of devices that were produced with this known trackball issue.
Some people like myself and StreetDocRN were lucky enough to get non-defective Tours.
It's the luck of the draw really. And people who hate their devices or have issues with them are more likely to be vocal about their issues than people who are happy and don't have any issues. So that's why you see lots of posts about the trackball and have heard lots of horror stories.
The optical trackpad is definitely the way to go though. No possibility of it getting stuck or gettting food, dirt or grime in there.