For the most part the airlines do cover the damages to your goods in transit and the insurance coverage is worked into the costs of the airfreight charges, however, they do not cover the freight charges incurred unless you buy an extra insurance coverage. This means that if you have a loss due to damages to goods shipped, the airlines will reimburse you for the invoice value of the goods shipped but not for the freight charges you paid!
As for your sea freight cargo, unless the exporter included sufficient Marine Insurance, as importer you are advised to purchase extra Marine Insurance. Before you buy the insurance, check what is and what isn’t covered! Make sure, for example, that ideally the coverage is All Risk, Warehouse-to-Warehouse, and that Civil Strife induced damages are covered should you be importing from or transit through a potential war zone. In any case, buy the insurance preferably from a US-based insurance company, for in the event of a claim there are good chances you’ll probably never collect if the policy was underwritten by an obscure insurance firm in some Third World country.
Bottom line is that while both the exporter and importer need to evaluate proper method for insuring shipments and handling Marine Insurance, assess “money risk” in order to minimize losses, cost of insurance will have to be prorated into cost of goods and for the importer too much insurance will ultimately result in increased “Landed Costs” of his shipment.