Yes, Kylie Jenner should have bought herself a new truck for her birthday--and any other present she felt like. As long as a wish does not hurt anyone else, and as long as a person can afford it, they should be able to buy themselves any birthday gift they want.
Kylie Jenner has the right to purchase whatever she wants with the money she earns if she first does the right thing with it. The right action is to give some money to a cause that is related to “the man upstairs” and perhaps share some with the unfortunate people in society. Other than that, she can buy a truck on any day she so desires.
If an individual, celebrity or non-celebrity, wishes to buy themselves a truck for their birthday and have the funds to do it, then they have every right to do so. This isn't a question of morality but rather vanity. If her followers on social media disapprove of her birthday purchase then they are free to post their opinion on her Twitter or Instagram feed.
Kylie Jenner can do whatever she wants, but the last thing she needs is a new truck. With so much poverty and tragedy in the world, it would be great to see reality TV personalities using their fame for good and reaching out to help others instead of spending more money on themselves.