I see two major flaws with your "test".
- As noted in your blog post that you linked to, this view is at 1:1 or 100% magnification. Any image is going to look near terrible at that magnification. Be reasonable in your analysis, and zoom out to fill your screen or similar.
- You are taking an image of a rubber nub. A rubber nub that is meant to be pushed and stroked by nasty fingers. Then when you are done using the phone, you shove it into a nasty pocket or bag. I would never expect a rubber nub to be dust and dirt free. Try taking a macro shot of a metal object like an award, or an insect, or whatever. But not a rubber nub.
You ask "How can I take professional looking pictures with a macro lens". There are a lot of ways that you could answer that. One might recommend better ambient or external lighting, or maybe a dedicated macro lens instead of extension tubes. Maybe a subject that is more interesting. You could also look at ring flashes or similar equipment. You could use advanced techniques like focus stacking and tripod+remote usage. Many articles exist already on the internet on basic tips for macro photography. You probably want to start with some of them similar to this: http://www.popphoto.com/how-to/2012/04/tips-pro-intro-tiny-world-macro-photography
As for your question, "how are advertising photographs captured". That is quite a different question. I'll refer you to a great example of how a photographer captures product photography for Apple computer here: http://www.theverge.com/2013/5/8/4311868/the-illusion-of-simplicity-photographer-peter-belanger-on-shooting