What a great question. Parenting has changed over the past few years and I think it is changing for the better, as long as we set clear goals and expectations for our children. I do agree that many of today's teenagers and younger children demand instant gratification. It is our job as parents to teach them to be respectful to self and others, be gracious and yes, experience disappointment sometimes to develop patience.
These things can be taught by modeling with our own behavior and expecting the same from our children. I do not agree with physical discipline and do not think it is necessary to raise good kids as long as you develop a strong bond with them and there is mutual respect.
Children become spoiled when they are given everything without any responsibility. Parents today work longer hours and often both parents work so they tend to be more permissive and allow the children more freedom because they feel guilty for the time they can't give them. It's when the parent-child bond is out-of-whack, that disrespect and resentment brews.
Parents may not be able to change their work schedules because they need two incomes to make ends meet. The solution would be to use the time they have with their kids to their best advantage. Spend quality time with them, talk to them - let them talk to you about how they feel, what their doing, etc. And give them a good work ethic, teach them to earn money and contribute for the things they want; video games, phones, designer clothes. Things are always valued more when they took effort to acquire.