Audio quality is another big factor with streaming media. Streaming media likes to heavily compress surround sound effects. While discs aren't perfect, they usually have a more immersive audio experience because of less compression
My understanding of a "conflict of interest" is that they happen when a personal interest interferes with a duty. Ex: a company executive receiving a gift from a potential supplier.
This situation would not be a conflict of interest because Apple has no duty to third party advertisers
The vast majority of products people buy help them solve problems of all kinds. An economic transaction is a win-win for both buyers and sellers. Look at products like the computer, the car, the telephone, etc. I think the world is becoming a better place as a result.