As for [2], I'd expect Andy Rubin's number is based on the number of tablets accessing Google services [4] (which isn't surprising since that is the number Google can most easily observe). Given that, it seems clear to me those 6 million count as sold.
[4] http://www.engadget.com/2011/10/19/googles-andy-rubin-six-mi...
[1] http://www.slashgear.com/googles-honeycomb-offensive-musters...
That means, to win in the US at the end of the year (since they're not competing internationally), Amazon has to beat:
* ~3 million Nook colors sold as of March 2011 +
* Nook Colors sold between March 2011 and the end of the year +
* ~1 million Android tablets sold through October 2011 (NPD numbers excluding TouchPad) +
* Android tablets sold in November and December
Theoretically, 5 million might be enough for Amazon, but you'd have to think:
* that Nook Color sales collapsed soon after March
* the Nook Tablet will flop
* Android tablet vendors can't even replicate their sales-to-date during the holiday season (even though there are new quad-core models and cheaper 7-inch models, among other things)
Personally, I think the more interesting race is Kindle vs Nook one-on-one. Nook, of course, has the early lead, but Kindle is selling faster. I think everyone expects Kindle to win eventually (absent a game-changing move by B&N), but will it be this year?
Given that outside the US includes Europe, Australia/New Zealand and the more affluent parts of Asia (Japan, Korea, Hong Kong, Singapore, Taiwan, etc.) and those are the places I'd expect official Android tablets to be selling, that assumption seems strange to me.
Putting this together, if Amazon hits their (rumored) goal of selling over 5 million Kindle Fires, they'll certainly get a substantial slice of the Android tablet market and quite possibly a majority among US users (depending on what you count, like Nooks). Nevertheless, there will still be a larger slice of Android tablets with Google services and the Android Market, and the Android Market will be dominant outside the US (e.g. if you believe the NPD numbers ASUS might well have sold over 90% of their tablets outside the US [3]).
[1] http://www.maximumpc.com/article/news/asus_eyes_18_million_t...
[2] http://www.theverge.com/2011/10/19/2500959/6-million-android...
[3] http://www.electronista.com/articles/11/11/22/npd.shows.hp.l...