Will certain retail channels refuse to sell non-UL certified products? Is the associated insurance liability outweighed by not having to pay for the certification?
UL isn't the only certification org in business but it is the best known one. If you are dealing with Security of Fire/Life Safety issues failure to have a UL or NFPA (National Fire Protection Associates) certification pretty much means you can only sell demo products and cannot get spec'ed in to any building system
Furthermore, lacking a UL certificate, if you are a powerline based device, odds are you will not be able to get liability coverage for your business of your product is not UL certified. So as Dale said, its not really a question of IF but WHEN.
its really a case that you probably cannot even GET "insurance liability" coverage unless you get a UL or NFPA cert.