Why do some pickles require refrigeration while other varieties do not?

Specifically, Claussen pickles must be refrigerated and yet I see lesser varieties of pickles that can be stored at room temperature. I understand that pickling was developed with the specific intent of preserving food, so I find it odd that a “preserved” food would require refrigeration.

Thanks for your replies.
You could say I’m in a pickle over a pickle, but that would be horrible pun…

I don’t believe they are “fresh pickles” that might require refrigeration. They are preserved and canned like all other pickles.
Seems it’s just a marketing ploy. A very smart one at that.

A properly fermented pickle lives in a brine of about 10% NaCl. Many people don’t like that much salt on their fermented cucumbers, so there are various low salt “pickle” recipes. Depending on the recipe, how much vinegar or other preservative is used, these may or may not require refrigeration.
The National Center for Home Food Preservation has a nice general description (plus recipes!) for various pickling processes: Preparing and Canning Fermented Foods and Pickled Vegetables