What I've found to date is that most of the apps in the green store are available in the beta store. Now having said that I also found on app that works fine in Win8.1 but not in Win10. So I suspect that the app maker is going to have to test their app(s) out in Win10 and make changes so they work in the new "Eco System".
Now does this mean that all of the apps in the green store will be in the beta store? Not sure but time will tell.
Source: New Windows 10 Insider Preview Build 10074 now availableWindows Store Beta improvements: We’re excited about delivering a single unified Store experience in Windows 10 which we’re talking more about this week at Build. We’ve made some improvements to the Store Beta which is now a blue tile instead of grey. Xbox Live games should be working and so are in-app purchases. Apps you purchased on a PC running Windows 8.1 will now show up in the Store Beta on Windows 10 as owned (and vice-versa). We’re also expanding the Store Beta from 41 markets with the addition of these new markets: Afghanistan, Åland Islands, Albania, . . .
My guess is that if I'm running Windows 8.1, I will see only apps that will run on 8.1. And, conversely, if I'm running Windows 10, I will see only apps that will run on Windows 10.
Of course, we all know that if Microsoft has its way, everything Windows 8/8.1 and all its detractors will quietly disappear.
I think Mystere, Wynona, and Kari are correct except Wyn when it comes to the database. They had to separate the Stores, or databases (they're simply databases) because some apps are OS specific as some pointed out. Store in 8 will always remain Store with its database and it seems to me they would have to rename Store Beta to something like"Windows Store" with its own database. Remember, Windows 10 (X) may be the last version of Windows to run across all devices.
Also, I would think the Store in 8 will probably be eliminated when 8 life cycle ends.
Please answer me this? > Why would they place apps in the 8 Store that are 10 specific? They won't run in 8. Would that not be confusing to a commoner? Of course there is the option that they could place them all there and describe what OS it will run on as all software has done for years. That could be a ploy to have users move on to 10, but I feel that MS has never been really good at marketing. Apple, to me, has that cornered.
Time will tell on this issue as with all issues.
As I said, my guess is that there will be one Store that will serve up apps to whichever OS you happen to be using, i.e. If you're using 8.1, you'll only see apps for 8.1. Conversely, if you're using 10, you'll only see apps for 10.
Hmmmm, which brings me to another guess. There could be one underlying database with two "forks"; one for 8.1 and one for 10.
Apple may have marketing cornered, but they haven't succeeded in getting me to pay way too much money for what I would get; especially since I have the ability to "roll my own".