Spot on, Gators!
Folks, traditionally for prizes of $1M or more the FL Lotto offers 2 payment options; a fixed payment per year over a given number of years (usually 25), or a one-time lump sum. As new games with prizes at $1M or more are released, the FL Lotto essentially locks in pricing for the fixed payment option with an insurance company. These financial products are referred to as Fixed Immediate Annuities, and are among the most stable annuity products available. If someone elects the lump sum option then the Lotto simply awards the $ amount it takes to purchase the annuity. As Gators has it, various fixed return investment instruments and US monetary policies in place at the time each game comes out can drive significant differences in the cost of such annuities. These differences have nothing to do with taxes or tax rates.
Think of it this way: If, at the same time the 500X came out last year you went to an insurance firm that sold annuities and said "what $ do I have to give you now to guarantee that you'll pay me $40K a year for the next 25 years?" Due to relatively low interest rates in effect at that time they'd say we'll do that if you give us $820K today. Now, just over a year later, that same annuity cost $640K, again due to higher interest rates.
One wrinkle. The FL Lotto is one of several that allow the resale of its prize annuities, so if the lump sum amount seems painfully low a prize winner can elect the annuity option and hope for more favorable future interest rates, and thus the opportunity to sell the annuity on the secondary market for a premium compared to the original lump sum value.