You're going to sound ignorant Stanley11, you cannot simply say that because it has never happened before, this is the first time something like this has happened then it's obviously a once off so why waste all the money? What happens if something like this happens again? Will you explain to the families and friends of the next 239 people why they're lives were not saving because of an assumption?
There is still a good chance this aircraft will be found, there are solid leads and items that can potentially be recovered that have been identified, they will not give up until they are positive there is almost no chance of finding it. The Inmarsat details have given them a credible lead, satellite images have found possible debris in the area they suspect it went down in and there are still a few days left for them to try and hear the pinger before it's battery runs out. So why would they discontinue at this point?
You're right, people die on the roads all the time and you know what? MASSIVE money is spent on preventing that, by thousands of authorities around the world, by all the major manufacturers, but hey, there are millions of vehicles out there driving all the time, billions of kms a year that they drive and only a very small portion of accidents so why bother with that either? Probabilities show it as having being infinitesimally small chances of it occurring...