This is almost certainly true for most plane crashes or ship sinkings.
However, it is not necessarily true of a car crash, and this is a common misconception. In most motor vehicle accidents, individuals do not die instantaneously, and it can take many hours or even days for death to be pronounced.
This is why, for example, people are more likely to die if their car crashes in a rural area than an urban one, where they have less access to hospitals.
If you have standby services in place, and they are able to get to the hospital in a reasonable interval, then this would not affect your preservation that much, in the absence of blunt trauma to the head or cerebral hemorrhage.
As an example of this, consider one of the most famous car crashes: Princess Diana, who died three and a half hours after a particularly high-impact car crash.
So, if you accept the premise of cryonics in the average case (obviously a big if), then dying in a car crash is not necessarily going to stop the procedure from being successful.
However, it is not necessarily true of a car crash, and this is a common misconception. In most motor vehicle accidents, individuals do not die instantaneously, and it can take many hours or even days for death to be pronounced.
I'm not a doctor, but I suppose that in most cases where death is pronounced after days the cause of death is traumatic brian injury, therefore even if cryopreservation can be performed immediately after death is pronounced the brain will be already extensively damaged.
Other cases of death in a car crash probably involve cardiac ...
I wrote a blog post arguing that people sign up for cryo more for peace of mind than for immortality. This suggests that cryo organizations should market towards the former desire than the latter (you can think of it as marketing to near mode rather than far mode, in Hansonian terms).
http://specterdefied.blogspot.com/2015/06/a-cryo-membership-buys-peace-of-mind.html
For those signed up already, does peace-of-mind resonate as a benefit of your membership?
If you are not a cryonics member, what would make you decide that it is a good idea?