Well actually you can, because Windows 10 apps are "universal apps" for any Win10 device; thus, the same App store is used by all Windows 10 devices. There is no seperate app store as there is with iOS and OS X - they're the same apps.
There's very little of worth in the Windows app store - why do you think Microsoft has spent big money on a porting platform for iOS applications to include with Visual studio? Because no one cares about developing for Metro. They missed the boat and are rushing to play catch up.
edit:
I'm willing to bet I spend more time dealing with Windows devices than 99.9% of this forum, it's my day job, and I'm half-way through developing our Windows 10 SOE for the company I work at.
Sadly the universal APP is still a myth. W10 is full of W8.1 APPs so no... you can't judge, because you are missing a lot of APPs that are only available for the Mobile version. Also a ecosystem is based in more things than the
amount of APPs you have in the store, there is cloud, data syncronization, comunication between desktop and mobile phone, continuum (now tell me that this isn't usefull), and again while people is obsesed with the amount... I'm more concerned about the
quality of the APPs you use on normal day: notes, music, camera (lumia camera), photos, file manager (I'm looking at you iOS), etc... vs iOS Photos, iTunes and company...
That said I wish Apple one day could do the same with OS X and iOS.
@IowaLynn I think I will end doing the same, but bootcamping W10 on the rMBP, there software here I really need and it's not in OS X.