March 2008: Wii sold 721,000. March 2009: 601,000. February was the last month of growth for Wii, and it began to collapse quickly after. April is not actually supposed to be a slow month, particularly when Easter falls within April as it did this year and last year (but not 2008).
PS April 2008 was 714.2K so I'm not sure what you're saying. Are you saying that the sales for the whole year, ie. including previous months, being higher than the same period in 2008 somehow mean that Wii is not losing momentum now?
Easter was tracked in NPD's March figures this year.
The rEVOLution is not being televised