Ths thread is a classic example of two groups talking not with each other, but next to each other - and both are right.
Group A says the Metroid fanbase should have been buying it by pointing to any individual customer. If you are a fan of Metroid and have a 3DS laying around somewhere, you have no excuse not to buy it.
Group B talks about the entire customer base as a whole, which has indeed walked away from the 3DS to some extent.