You can turn over any size tractor if you do something stupid. Even lawn mowers. Do I need a ROPS on my CC 1046? Absolutely not! And if it came with one it would be removed. I'm surprised though that lawyers haven't convinced manufacturers to put ROPS on all sizes of tractors large and small.
I'm not saying ROPS doesn't do it's job, it does work well. But more times than not, I find it to be an annoyance. Besides, no piece of metal can replace the safety knowledge in my head. In the 25 years I have been driving tractors(yes my grandpa started me driving when I was 5! I can just hear the lawyers screaming now!) I have never once been in a situation where I would have rolled a tractor. Grandpa taught all his sons and grandsons what were safe and not safe things to do on a tractor and he expected us to learn and be responsible. Be smart and be safe and you'll never need a ROPS.
BTW, most of the tractors I learned on were 1930's and 1940's model John Deeres. No ROPS on those. Most of them did have a hand clutch though, so that was a nice feature for a kid with short legs /forums/images/graemlins/grin.gif