I think that software usability and quality can be related, but not in every case. Usability describes how easy it is for someone to learn and use the program without much complication. Software quality is how well the program is presented and how well the program actually performs the tasks it is supposed to. One of experts said that "I would rephrase useability as "how well the software allows you to do your job" There are many websites and applications that were a snap to figure out, easy to use, but absolutely got in the way of processing orders, recording data, and so on. But
even if the software can perform the function it needs to, if it gives me a harder time than necessary than it won't rate well quality wise. There are a lot of analogies that can apply here, from cars to tools, and in all of them, usability almost always denotes quality.
Think of a car with wooden seats, no power steering, and uneven pedals... hey, it gets the job done doesn't it but how would you rate it quality wise? Any thought??