Mt.Gox was an inside job. Even if they had been insured at the time the insurance company wouldn't probably have paid anything to the screwed users because the money ended up in Mark Karpeles'es pockets. Now it will be interesting to watch how they will distinguish between an inside job and a genuine breach of security.
For exists the ensurance for sure they have a team that will analyse each problem the exchanges may face, and will check the code first, makes no sense give protection to a new exchange that can easy hacked, i do hope this ends with the problem of exchanges funds lost to hackers.