I wish we could get Silent Hill Homecoming's 1st NPD for comparison. The only thing I can find is that the PS3 version was number 10 on the PS3 top 10, 360 version didn't even manage that (but somehow Infinite Undiscovery did, lol).
We do have NPD totals through Jan 2009 though (PS3 = 84k, 360 = 73k). That's 5 NPD reporting periods, which makes Shattered Memories 40-50k 1st NPD probably not look so bad in context.