If you don't think R* will take away the gifted money think about this.
What if a store only sold their merchandise to people who buy store credit or earn it through rewards, (ie, joining a membership with the store, or referring a friend). And image if a thief stole in-store credit.
Do you think the store will allowed stolen currency? Absolutely not, they would refuse service and someone handout punishments.
Yes there is a little difference between the two, but the they're more in common than you might think.
I don't blame R* for wanting to reset the cash. They loose a lot of money with nobody buying cash cards. I think buying virtual money with real money is crazy, but I understand how a company works and their goal is to make as much money as possible.