When you're making a big purchase you like to know that you've got some assurances that things will work out as expected. That's why we have warranties, so that if anything goes wrong you're not left empty-handed.
SSL is no different. When you're securing your website with SSL what you're actually protecting is your customers' data. When that data gets compromised, as has happened many times before, customers tend to react angrily–sometimes even litigiously.
That's bad news for you, especially if you had nothing to do with the data breach or security lapse. This is why SSL Certificates typically come with a warranty. In the event that anything goes wrong on the Certificate Authority's end, you're covered by your warranty. This could mean a mis-issuance or some catastrophic failing of their SSL protocol. Either way, you don't need to worry about it–you're covered.
