kishna, i would say that anyone who didn't select 7700 for an emergency descent must be the one who fell unconcious. The last thing the pilot wants to do is try to make contact with ATC, especially with dinner flying across the instruments. You're going down regardless to FL100 (or below), just slap on the squalk and at least we have a chance of getting everything else out of the way.
7700 in my mind is made for radar to see 'we're in the ***** and can't do much, get everything the !!!! out the way'. It highlights the fact something very serious is happenning by showing other areas to keep traffic away, and don't bother me, no phone calls or other things, I just ain't interested.
Other urgent matters which can be discussed on the RTF before anything happens have no priority to get 7700 selected. ATC can use their discretion then, and retain a full set in the data block on radar. The time we put it on is to alert other areas or agencies, for instance Approach, Military control (including danger areas), D+D cell, other FIR's, and even just other sectors which you may be getting close to with a direct routing.
That's what I think, but it is getting late........ <img src="smile.gif" border="0">