Sharper Image caters to a specific type of person -- the same type of person that companies like Bose do....
This is the type of person who is "upper middle" class, makes a decent living, but tends to be too busy to do their own research into what products they should by. They rely on brand names to trust, because they just want to shell out their money and enjoy.
I also think these people are good at talking themselves into believing what they have is the best. How many times have we been at someone's house and had a Bose system demonstrated? I remember the first time I heard one of their "Acoustimass" systems at a friend of a friend's home. He cranked it up to unbelieveable levels of distortion and resonance of cheap plastic parts, and was like "Doesn't this sound great?!"
I can kind of understand the overall concept. I work hard and make a decent salary. At the end of the day my brain is pretty toasted. I just want stuff to work and work well. BUT, whenever I make a purchase (at least in the realms of audio, video, or other electronics), I still take the time to do the research and make an informed decision. I think a lot of other people in my "boat" do not.
That being said, I've been to Sharper Image a few times and seen some rather interesting gadgets. I've never once felt compelled to buy anything. I do understand they have a good no-questions return policy that rivals or exceeds most other places. I wouldn't buy headphones there though.