Startup jobs are one of the best places for learning new skills and expanding knowledge by doing things, solving problems and getting things done.
A job in a certain function of the startup will give you the skills necessary to know how to get things done in that domain. There is scope to fail and experiment in startups like no other place.
Startups grow aggresively and very quickly and this gives the employeees a chance to flex their muscles take up larger responsiblities and grow quickly to the highest levels of management and leadership. This is entirely different from a routine corporate job in which career accelaration is slow and dependant on a lot of other factors rather than the potential of the employee and their ability to push themselves and do things.
They are great breeding grounds for future entrepreneurs. If you want to be an entrepreneur there is no better practise ground tha joining another fast growing startup with a small team and see first hand how things can get done. This learning is unparalled and can never be gotten from any other place. This would also give people the courage to make their own leaps and build their own companies.
Icentives and Money - Startups offer more than a salary, they offere equity and options which practically make you a part of the ownership strcutre and the success and growth of the startup is aligned to your own rewards and motivations. You build real value through your work at great startups and also have the option to reap great rewards.