I'm not sure how accurate this is but:
http://gamrreview.vgchartz.com/sales/38506/gray-matter/
This has alleged PC sales for the first 6 weeks at 7,305. I'm not sure but that seems quite low? However, I'm pretty sure that wouldn't include digital copies (only physical copies) that a lot of adventure gamers buy from sites like Adventure Shop.
Xbox360 sales also not on that list.