When you say "DChoc Sudoku is missing, which is odd considering how well DChoc Solitaire sold.", take into account that as Sudoku was released late January, in the few days of availability it can't have made much of an impact on the total January charts.
Yeah, I suppose so... Solitaire took a while to get going too.
It's just a bit of a struggle to find something interesting to say about the charts when there are so few new entries... It's always tetris and flipping poker! :-)