Violating the terms of the license that you agreed to when you purchased the IP can result in severe civil and criminal penalties. Civil penalties can be up to $150,000 per infringed work, and criminal penalties can be up to $250,000 and jail terms of up to five years (in the US).
No, I'm not saying that you're going to go to jail, but think about this. Developers invest a lot of time, energy, and often money into the apps they create. Musicians do the same with their songs. Movies..... You get the idea. They do this with the hope of realizing a return on their investment. By stealing a song, an app, a movie, you are taking from that IP creator something that you do not own. When you're talking about a $0.99 song or a $1.99 app.... How much is that compared to what you give to the phone company for the phones (plural, since you're talking about sharing) that you carry around?
Is what we have the best possible scenario? No. Perhaps there should be a family plan. Perhaps that is something Microsoft should consider. Given that it sounds like a lot of people from iOS (I haven't heard of talk about this on Android, but it wouldn't surprise me that it's there, too) do share accounts, I suspect that this subject is just going to get more and more attention. If the agreement between the purchaser and the seller allowed for sharing, then this would be a non-issue. But given the climate that the music and movie industry has created, I doubt we'll see that... Though I could be wrong. With apps, however, it's a different ballgame. There is no "app developer industry association" so basically Microsoft could muscle the developers and change the agreement they have with them. Then they could change the agreement that they have with users, and allow sharing between family members. But in muscling the developers, you may see developers leave, and Microsoft doesn't want that, do they?
As a developer, I don't think I'd take too kindly to the super monster software conglomerate telling me that from now on I get one purchase price (of which they already take 30%) for the sale of my app to a whole family, where I had been getting it from each person who wanted my app. My response would probably be along the lines of "just who do you think you are that you think you can tell me what I am allowed to sell my apps for, and under what conditions???" Then I turn all my apps into free apps (so MS doesn't get a dime) and switch to an in-app purchase model, where you can go install the app as many places as you want, but each instance has to be paid for or it won't work. Yeah, I don't think that'll go over too well. Besides, Microsoft isn't in the muscle business.
Someone else posted a comment that I really liked, and I'm open to the idea. Create a family plan, where you pay more than the single price, perhaps double price, and you're allowed to install to anyone in your family's phone, given limitations that are still open to discussion. Limitations such as who counts as a family member, how many family members are allowed as a maximum, and so forth. The suggestion that I threw into that discussion as a limitation was that since MS already has the Family Security program, whatever it's called, they already have framework of parent/child relationships. With that in mind, and given that those parents are allowed to see the child web surfing history and such, you could say make a family only allowed to have two adults, and x number of children, and the child accounts would be fully open to be seen by the parent accounts (discourages you from sharing with Joe the neighbor as a child, if he doesn't want you to see his history).
I'm not a lawyer, so don't expect that this is a comprehensive overview, but just the words of some guy, who knows the subject better than the average Joe, because knowing this stuff is in my interest, and I've done the best I can to make it understandable, even though I may not know all of the caveats.
Now here come the trolls to berate me, once again, because I want to live in the utopia of people actually obeying the law, and respecting other people's property - even their intellectual property.