I'm not sure the WII was in the same generation as the PS# and Xbox (I have all three, btw). It's tough to compare because Nintendo was selling older technology before the Xbox then PS3 were on shelves. Lower price and specs with a completely unique (at the time) user interface contributed to excellent sales and initial market domination. WII sales have dropped off while PS3 and Xbox are winning current quarters.
But that wasn't my point.
Microsoft entered a market dominated by two established players and within a few years is selling more units (per month) than either. Redmond stumbled mightily out of the gate -- choosing the wrong HD format and missing out on the interactive idea -- but pushed on to establish itself in the market.
Ditto on Zune. The Zune is an excellent media player but MS failed to market and support it properly. That doesn't mean they will not succeed in the media market place.