Unless your users are running the Enterprise or Education editions of Windows 10, the Windows Store is mandatory. This essentially means that any small business, running Windows 10 Pro, cannot block access to the Windows Store and that end users will have unfettered access to download and install apps.
This is a retroactive move by Microsoft. Originally, Windows 10 consumer (Home) was the only edition that couldn’t block the Windows Store through Group Policy or registry modifications.
A Microsoft Knowledge Base article (KB3135657) from April 6, 2016 notes the change. The change is a result of the Windows 10 version 1511 upgrade.
@SwiftonSecurity was one of the first to unveil the KB article to give it the fanfare it deserves.
Microsoft retroactively removes ability of companies to turn off Windows Store in Pro version of Windows 10 https://t.co/45k4NA0aoI— SecuriTay (@SwiftOnSecurity) May 3, 2016
Mary Jo Foley received a follow-up statement from Microsoft, confirming the change:
Microsoft is focused on helping enterprises manage their environment while giving people choice in the apps and devices they use to be productive across work and life. Windows 10 Enterprise is our offering that provides IT pros with the most granular control over company devices. Windows 10 Pro offers a subset of those capabilities and is recommended for small and mid-size businesses looking for some management controls, but not the full suite necessary for IT pros at larger enterprises. The ability to block access to the Windows Store is typically for organizations who want more control over corporate-owned devices. This fits into the value of Windows 10 Enterprise.
For those computers not covered under an Enterprise or Education licensing agreement, Microsoft has to recoup its costs for offering a free upgrade. It seems it believes that the Windows Store is part of that revenue recovery effort.