I'm seeing more and more manufacturers, especially smaller ones, forgo the UL approval process. This is a situation brought on by UL themselves.
First, understand that UL is not a government agency, and there is no law that requires any product to be UL approved. I'm not sure what the NEC has to say about that, but the NEC rules are not U.S. laws either.
UL is very inconsistant. They have offices over in asia where you can get away with alot. There are also alot of products coming into this coutry that have a bogus logo.
Here in the U.S., UL test labs are run pretty inefficiently. It is like dealing with the post office. Some of those folks work at one speed - slow.
Another problem is their rules can be very ambiguous, and subject to alot of interpretation. That's why some manufacturers feel that as long as the components are approved, they are OK. It's probably what thier local UL lab told them.
Other offices are more strict, and won't consider anything OK unless you've paid them a few thousand, and they issue you a UL number.
There are also alternatives, TUV, CE, CSA that are perfectly acceptable to most.
Many years ago, UL used to buy the manufacturer some level of protection on product liability, but these days, anyone can get sued for anything. The best bet is to design something that is safe, use your own brain and don't do things like exposed AC connectors, and have good insurance.