According to this MSDN article, Windows 8 apps can be installed through the Windows Store (users choose apps) or through sideloading (administrators choose apps to deploy).
Is there an option for users to choose the apps they'll like to install in an enterprise intranet environment?
Not as such, no. I think Microsoft's idea is that you use the sideloading mechanism, or possibly that you deploy the apps to the store and only allow your own users to install them.
IIRC you can manage this better (I won't say 'well' because the whole thing seems very clumsy to me) via SCCM 2012.
Windows 8 and Windows Server 2012 computers joined to the domain can access the Windows Store, and users can install apps from the Store, unless you have set Group Policy to disallow access to the Store. Like any other GPO the restrictions can be applied to users or to computers.
The article to which you linked describes a process by which you can deploy Metro apps when you want to be sure they are preinstalled on users' computers, and/or when you are disabling access to the Store. In these cases you would obtain the app directly from the vendor, rather than from the Store, or develop it in-house, since you cannot sideload apps from the Store.
For more, see Managing Client Access to the Windows Store on Technet.
