This is a totally a marketing technique to make users feel more secure. It's no different than plastering the "hacker safe" (now McAfee Secure) seal on the top of your website. (Which by the way, in tests I've seen split-testing proved the old "hacker safe" seal works better than the new one, or at least it did when the new one was first released).
Most of users don't know what SSL is, but they sure as hell feel more secure if you have a big lock or a nice green checkmark in the top corner, especially if they're thinking about putting in their personal info or credit card number.
Full disclosure: I'm a founder of an online marketing company. :-)