> The insurance covers losses due to breaches in physical or cyber security, accidental loss, and employee theft.
I'm not convinced that this even protects the online wallet against Mt Gox style corporate malfeasance, where much of the damage was done as an intentional corporate decision by the leadership. (I'm conjecturing that's what happened at Mt Gox; regardless, this seems not to cover against them trying something intentionally with their coins related to trading, and then losing them all.)
Additionally, as you pointed out, this only covers a very small portion of their holdings - a percentage smaller than the number of Mt Gox coins that were "recovered" (about 25%).
Finally, Coinbase being insured against the value of the bitcoin loss doesn't translate in to you being covered, as Coinbase may accrue other debts they have to pay off before your holding in the event of a hack large enough to cause a serious business disturbance, such as paying off creditors with higher standing.