This was the case in the past. However, like Satrina says in the post this is information based on what we knew in TBC before the changes made to crushing blows.
He also say that based on information we knew then, that the loss of 200 defense would push you into the realm of every not avoided or blocked hit would be a crushing blow. This is not what we have observed while completing this encounter. We are being crit but not crushed. So Satrina's "If nothing has changed..." statement is just that. Things have obviously changed. If things were like we knew in the past, we would be seeing crushes and not crits while under this debuff.
In order to see if things are indeed the same we would need to actually work with lower levels, and because it was our unmodified base defense skill in question, and not our modified (rating enhanced skill) that was being used for the old crush calculations, this hypothesis is not easily tested.
Basically, I was wrong when I said it was based solely on level disparity and not skill, however the statement is still correct. The system is based on your base defense skill which your level is the sole factor to determine this. What you need to remember is that even though you may be 540+ defense, because your gear has rating that improves your base skill level, the system only uses your base to determine crushing blows. If it used your enhanced skill level, there would be no reason to worry about them at all.

