In the study of Human Geography there is a concept called sphere of influence.
What this concept tell us is that various trades have different ability to draw customers/ number of customers required to sustain business.
On the one end of the scale is the provisions shop which has a very small sphere. In fact some don't stretch beyond the HDB block they are located in. They are able to attract enough customers that the provisions shop in the next block is not a threat. Why, because the good they sell are purchased based on convenience.
At the other end of the scale we have luxury goods. These can include guitars, jewelry, branded goods etc. To run a business selling these goods you need a broader market as not everyone will purchase and most people will purchase infrequently (not many of us buy a new guitar every week!)
Therefore guitar shops have a large sphere of influence so they will tend to locate at the area that allows them to cover the greatest area. Which equals town (thats why it became town in the first place!)