Could it be that it was because Bellagio, Treasure Island, Beau Rivage etc. were all under a company called Mirage Resorts. Mirage would have been a flagship property, actually the originating property for Mirage Resorts. However that might have little value to MGM itself. I would think that the Mirage name had as much to do with MGM for the whole group of properties, including TI and Bellagio and their identity with Mirage.

Not saying that there could be any truth to this subject but it is my understanding that the Mirage name is simply that they acquired Mirage Resorts. If they wanted to, they could probably strip Mirage from their name entirely. Like
AOL Time Warner reverting back to simply Time Warner.

I haven't read the thread because I have just chalked it up with internet misinformation in the wake of S&R but I have noticed a thread running on USENET that has been saying that The Mirage is going down hill. If that were to be true and the property was a strain on the company as a whole they might have an interest in cutting it loose. Personally, I would really doubt that though. Also I wouldn't put any credance to it unless you see MGM Mirage start to move toward changing their name back to MGM. They certainly wouldn't keep Mirage in their name if they were intending to sell that name off.