I think dividing it by the country's computer-using population is not helpful because this is already the number of client downloads and we probably only care about that magnitude (unless you want to know per-capita bitcoin users for trivia).
Which of those two groups would be more important for the
community:
- 1M of 20M nation (5%)
- 2M of 400M nation (0.5%)
I would say the 2M

I understand your point, though. Having 100 million users in Japan would be a very dynamic than 100 million users in India.