There's a lot of confusion and misinformation about the compensation structure on this sub, so I'll clear it up:

Month 1: First year signing bonus, paid in full. Month 12: 5% of initial RSU grant (paid on the 15th day of the month). Months 12-24: Each month, you will receive 1/12th of your second year signing bonus, included with your normal (base) paycheck. Month 24: 15% of initial RSU grant. Month 30: 20% of initial RSU grant. Month 36: 20% of initial RSU grant. Month 42: 20% of initial RSU grant. Month 48: 20% of initial RSU grant.

The basic idea is that you have a total compensation target which is derived from some combination of salary, cash bonuses (if any; usually signing bonuses only), and RSUs. It does increase each year, especially if you get a promotion and/or strong performance review scores.

Some important points:

• Your base salary will not decrease. It'll actually increase slightly to cover inflation (unless you get promoted; it'll increase significantly until you hit the cap). Not sure where you (or your recruiter) is getting that idea.
• You might look at your offer and think you're going to make less money in year three than you did in year two, since 40% of your RSUs are worth less than 15% of the RSUs plus the second half of your signing bonus. In truth, the RSUs that you get are actually forecasted to increase in value by some amount (15% or something, as I recall) each year. This is where most of your "raise" will come from each year. If the stock fails to perform to the forecast, they'll usually grant additional RSUs to cover the difference (with the caveat that these still have a vesting period of their own, though it's usually only a year). If the stock exceeds expectations, they'll often use that as an excuse to deny salary adjustments and refresher grants (so if you're getting X RSUs this year at a price such that you exceed your original compensation target, too bad--that's all you get).
• The signing bonuses are intended to act as a surrogate for stock in the first two years (the assumption that the vesting schedule is backweighted to ). This is by design, both because signing bonuses psychologically contribute to the endowment effect in employees, and because it gives the granted RSUs more time to appreciate with respect to the forecast.

Why is the compensation structure designed like this? It's incredibly cynical to think it's intended to confuse employees and/or rip them off, especially since it really isn't that difficult to figure out. I'm not an accountant or lawyer, but I'm guessing there are tax or cost implications to this approach that save the company money, albeit at the risk of significant turnover during years that the stock performs poorly (it's also worth noting that Amazon is incredibly good at manipulating Wall Street, and for good reason).