Amazon is rumoured to be extending its retail enterprise in a surprising way, opening up an Android app store to work alongside what's said to be an Amazon-branded Android tablet.That's the claim of TechCrunch, which says plans are already well underway for the store in the US, which also makes a UK store a strong possibility further down the line. It also claims to have a tip off for that Amazon tablet, but doesn't have any information more than that.But a tablet would make sense if the company has detailed plans for an Android app store. After all, the Kindle did well in terms of hardware, why not jump on the tablet bandwagon too?According to TechCrunch, there would be a 70/30, or 80/20 royalty split, a $99 subscription fee for developers, DRM tagging by Amazon so apps only work on Amazon-approved devices, an option by Amazon to pull anything unsuitable from the store and finally, a selection of free apps.Some of that sounds a little restrictive, but if the hardware is cheap, you might well get a few takers for it. More on this when we have it. With the sound of things, progress is well underway, so we might see something around the start of 2011.