I found out there was a difference when I was doing my first cook on the 22.5. I loaded her up with coals, and put the chamber on top with the water pan inside. Filled the water pan, and then grabbed one of the grates (not knowing they were different) and put it on the bottom. I place the meat on that grate. A couple of hours later, I needed to add the other meat I was cooking. So I went to put the other grate on the top and I then realized it would not fit and I was in trouble. I had to unload all of the food from the bottom, switch out the grates, and then put the food back on. I figured, hell, if the grates on my ECB were the same, then why wouldn't this Weber?
Since then, I've paid closer attention to which grate is which. It just didn't make any sense to me as to why Weber would design it that way which prompted my phone call to Weber Support.