Yes, tenure equals lifetime employment. However, consider the following:
1) Compared to other professions that require equivalent education, academics earn lower wages. This is clearly a choice for many of economic security and a more flexible work schedule over increased income. But it is a choice with real economic costs.
2) It's not like getting a tenured position at a top-drawer school is the easiest thing to do in the world. You have to get accepted into a good Ph.D. program, write an excellent dissertation, demonstrate an ability to generate research of high quality and quantity, and trust your luck that these skills will be recognized by your senior colleagues inside and outside your university.
3) I can't stress this enough -- a professor's wage is almost entirely determined by the market. Yearly raises in our profession range from infinitessimal to nonexistent. The only way to earn big raises is to demonstrate our value to the outside market by getting a competing job offer. That's about as real as you can get in terms of the wage structure.