couple questions...
1) why does one want something so short?
2) how'd you get the ash catcher on the 18"?
Good questions: Why so short? I keep the 18" in one of my sheds and with the stock legs, I have to keep it on the floor. With the short legs, I can just set it on top of something (like my table saw) in the shed and it'll open some floor space. Additionally, to take camping, I can just lay the shortened 18" on top of other stuff in my truck rather than fiddling around removing the legs to make it fit in the bed of my truck.
The ash catcher? I found it on ebay awhile back for around $25. I personally, HATE the original saucer pan (on this and the 22"), so I got the ash catcher.