I'm not sure if this will be much more work, but there's another way of doing this that gives a more precise number.
We still have the full "yearly" from VGChartz. And while we may only appear to have the top 100 games, we actually get far more than that. In fact, I think we might even be getting the top 500, or something like that.
The 100th best selling game so far this year is Batman: Arkham Asylum at 94k. If we search individually by platforms or publishers, however, we can see that Nintendogs has sold 23k, that Gran Turismo 5: Prologue has sold 11k, and that Valkyria Chronicles has sold 9800 copies.
What I'm suggesting is, essentially, that you write all the games, that have sold, say, at least 10,000 units this year. Then, next month (or week, if you want to do it that often), you do it again, and calculate the difference.
This is probably a lot more work (I imagine it should take around 2 hours each time, at least), so I suggest doing it monthly, rather than weekly. You could also arrange a group of people to help you, say for instance making me put all the Square-Enix and Nintendo games into excel, while Gilgamesh puts in Electronic Arts and Activision, and we both mail it to you.
I propose that instead of making it weekly, you do it monthy and quarterly instead (and then possibly weekly during peak seasons, or under special circumstances). You'd be getting numbers down to the very last digit, instead of just down to the last 1000. It would be far, far more interesting, and overall it shouldn't take any more time (as you'd be doing it far less often, with longer time spent each time).
It essentially means we'll be having a poorer weekly than we used to, but an equally good monthly. And that's really not such a huge loss.
