Thanks for your response. The number of PCs you can install a purchased app varies from app to app. Thanks for your remarkable feedback, we will pass the info to the appropriate team.
Cheers,
If the restrictions vary app to app, it would be useful if the windows store lists the limit when purchasing each app.
I won't drop as much (if any) money if it can't be used on more that 5 devices. (Ideally 5-6 users on the same 5 devices). You could even list the relationship of family members somewhere online. In gmail they have spots in the address book for listing relationships. I'm not sure the function of this (probably something to do with google plus), but it might be used by microsoft (if you made an equivalent) to store who is immediate family, etc.
Here is the Blog Post that explains Device Limits for Apps in Windows 8.1