Does this make the practice any better?
1. A competitor offers an alternative product at a better price. 2. Sennheiser produces these more efficiently than anyone. 3. All alternatives have similar margins. 4. No other manufacturer has a similar product.
Whatever the case may be, it will inform the rational comparison shopping process. This is a discretionary item. There's probably some economics name for this, but it's not insulin. Sennheiser isn't coercing anyone.
Same logic after reading and accepting the comments above.