Bookseller Barnes & Noble (BKS) has only been selling apps for its Android-running Nook Color e-reader tablet for about a month, but already the device’s app store has crossed the million-download threshold.

That’s a whole lot of downloads for a tablet that started its life as an e-reader, and they’re all Android downloads, as the Nook app store went live with an update to Android 2.2 Froyo. That update came at the end of April in the U.S., and since then, the store has seen an influx of games and other popular Android apps – including Angry Birds.

In fact, Angry Birds holds the top spot in the store, according to a press release. Of the top five apps selling in the Nook Color store, four of them are games: Angry Birds, followed by Solitaire at No. 3, then Aces Jewel Hunt and Astraware Mahjong. Holding down the No. 2 slot is Drawing Pad.

In fact, according to the press release, the Nook store hit a million downloads in just one week – which is weird, considering it has been available since April and hinting that perhaps the store hasn’t been fully functional for all customers up until recently. Still, if the Nook app store has only been available to all for about a week and it’s seeing these kinds of numbers, it suggests some pretty strong demand behind both the Nook Color as a tablet and the apps it’s making available.

In the press release, Barnes & Noble CEO William Lynch makes it sound as though the bookseller is going to continue to expand into the app space and increase the size of the store.

“We’re building on the early success of our Nook Apps offering by scaling our collection of popular apps with the thousands of developers who’ve approached us, while ensuring we continue to deliver the high-quality experience Nook Color is known for,” said Lynch in the press release.

The Nook also has pricing on its side – it runs just $249, which makes it a pretty cheap 7-inch tablet (although it lacks Android 3.0 Honeycomb, which was designed specifically for tabs). Apps in its store are also pretty cheap, according to the release, and hover between $2.99 and $5.99 for the most part.

It’ll be interesting to see what sales numbers Barnes & Noble is pulling down with the Nook itself and what the demand for the tab is like. One can’t help but wonder if, with the Nook as successful as it appears to be, if Amazon’s (AMZN) rumored tablet isn’t waiting in the wings to join the fray.