Many years ago as a tyro pilot with an engine failure I did not call it as I was confident enough that I would glide to the airfield and effect a safe landing and didn't want the added pressure of fire engines and everyone watching. I landed and snagged the aircraft - end of story. BUT what if the ATCO was packing them in tight and wanted me to overshoot. What if I had overestimated my ability and made a smoking heap short of the runway? It would have been MUCH better to have everyone in the loop and ready to act in the event that it all went horribly wrong. I have made lots of emergency calls since then and been glad of the company by the time I get to the runway.
As a grizzly old ATCO I have instigated emergencies many times for no more reason than the "feeling in the water". I have justified it to angry airline pilots, who didn't want their passengers worried. I would hapily make 99 unnecessary calls for the 1 time the fire crew can be at the burning wreckage 2 minutes earlier. I will not have on my conscience the pilot (and passengers) who survive the crash only to burn to death. Those without conscience will also be swayed by the subsequent board of enquirey (or litigation) where they will be asked why they did not consider a vacuum failure to be an emergency situation for the one person who does turn it into a crisis.
BEagle et al, you have to accept that not all pilots are as experienced as you. For some pilots merely getting lost or becoming disorientated would be good cause for fire standby. If a confident sounding pilot goes out, becomes unsure of thier position and so "shook-up" that they can't even work the radio (to get D&D help), what is the odds of their making a safe landing?
ATC see (witness) more landings than any pilot and when they are starting to scare us in the control tower it is time to have the engines out any waiting. When it is written in black and white in our procedures to have them waiting (for certain weather conditions) it would be inexcusable not to.