There are always ways to get around the law if you want to. They should have left the principle or spirit of the law in place rather than define a specific action as fulfilling the principle. We do the same thing when we make a rule that you can't drink any alcohol. The Biblical principle is that we keep the Holy Spirit in control and not get drunk and be controlled by the alcohol. So we don't drink but substitute alcohol with something else.
Many people do plan for their earthly retirement.
But most Christians are not planning for their heavenly retirement. This is the point of the parable. The Point Christians ought to be shrewd in their stewardships and use earthly finances to make heavenly friends. Do you realize that when your stewardship is finished here on earth, you will have to leave everything behind and go to a place where the only thing you can send ahead are people. We derive our understanding of the relationship of the parable to the Kingdom of God from verses 10f.