All Ardross said was "The hopeless Cattermole again", Shadz. Which, as I read it, was for not mentioning the horse was out of the running, not whether his legs were broken or he'd started juggling firesticks while riding a unicycle.
I don't think commentators should say too much about any incident in running, whether they're commentating for the course or ATR or RUK - although if it's blatantly obvious to spectators who see a loose one come by with a swinger, then the caller has to say something like "unfortunately, XYZ appears to have picked up a very serious injury there" more out of acknowledgment than anything else.
I do think callers must note, though, when horses leave the race, for whatever reason. But not necessarily why, if it's sensitive. Provided, of course, that they actually see the incident! I'm not sure that all courses give a perfect view and in some weather conditions I'm sure it's very difficult at times to note what happened back in a big field.