Regarding the evacuation at Sydney - if there is the possibility the aircraft may be on fire, then it is very important to evacuate the aircraft quickly. As it turned out, there was no real danger. However, how are you supposed to know this on the spot when you are told there is smoke coming from the wheel assembly. Should you wait a few minutes and see if the things roars into an inferno before getting people off? Of course not.
I call your attention to Saudia flight SV163 on 19th August 1980. A fire broke out in the cargo hold just after the aircraft had departed Riyadh. The aircraft was turned around and landed at Riyadha. However, the crew elected to taxi the aircraft off the runway, and shut down the engines, before evacuating. The end result was that the inside of the aircraft burnt out, killing everyone on board. You can read more about it at http://aviation-safety.net/database/1980/800819-1.htm
If the possibility exists that the occupants are at risk, then they should be evacuated as quickly as possible. It is a lot easier to look back afterwards and decide whether risk warranted an evacuation, than to evacuate panicked passengers from a burning and smokefilled airliner.
Osteogenesis - I think it would be a wise idea to let the crew know of you condition, probably give them a letter from your doctor, just as it would be to let them know of any medical condition that may be relevant to the flight. However, I would suspect that in an emergency evacuation, you would be sent down the chute just like anyone else.
"So powerful is the light of unity that it can illuminate the whole earth." - Bahá'u'lláh