That's a different source though, and figures for the world not the US, so not directly comparable.

Neilsen do update the figures every so often in items on their blog, but that was the latest historical graph.

This entry from last month has the figures for June (so six months since the last figures shown on the graph) Android up 14 points to 40%, RIM down 8 points to 19% and Apple still steady at 28%:

http://blog.nielsen.com/nielsenwire/online_mobile/40-percent...

I believe someone on hacker news was copying these monthly updates into a spreadsheet so they could make their own graphs without having to buy the full report and sharing the results, you might be able to find a link if you search.