It's not. The windows store is limited to their provider. The linux system allow any provider to plug itself.

And what about all the real apps and not the toy phone apps?

You can distribute bog-standard desktop software through the store: https://msdn.microsoft.com/en-us/windows/uwp/porting/desktop...

Last time I looked into it you had to to some porting too, it didn't really work with "bog-standard" as claimed.

No, they work as-is most of the time. You just have to make sure you're not writing to your install folder or try to install services or something like that. The use of UWP APIs instead of/along classic desktop APIs is completely optional (and most of them are supported out of the box even without the bridge, the exception being the APIs that require app identity, like Tiles or supporting a Share Target contract, at least not in a easy way)