Originally Posted by yepimonfire
if it changes the shape of the driver it may very well change the sound, but probably for the worse.
personally i say they are idiots for doing it.
Actually, There may well be some logic to this. Sound waves propagate in a radial pattern, and where they collide they either interfere constructively or destructively, creating a single "perceived" wave made up of the components of all the individual waves. Now, by creating a concave indent in the surface of the diaphragm, there is a higher density of waves per surface area in the center, where they are colliding and focusing into a more coherent wave. Now, this "single" (not really single, but this is a simplification) wave will have some unique properties. Yes, it will be distorted an amount, because there is now cancellation between various frequencies interacting, but, depending on the size of this indent, there will be a certain frequency or frequencies at which the sound waves from the surface sum together and create a wave of greater magnitude via constructive interference. Given that the width (and therefore depth) of the indent is macroscopic (made by a probing hand or pen or what not), it would likely create a boost in the bass region of the frequency response of the diaphragm. Also, by adding non-linearity to the surface, the diaphragm would become stiffer, and thus might also aid in bass reproduction.
Now sure, this is going to create distortion, and frequencies near the frequencies being amplified are going to be canceled (this is what causes bass "bloom" and "bleeding" into the lower mid frequency spectrum), but in the end, it certainly would reason that this gives the earbuds more bass.