I found a Toyota web site to confirm the information provided by JZ Twins, above.
It says, for the True Start:
* 84 month service replacement warranty
* Years 1-2: 100% of parts, service and towing
* Years 3-4: 50% of TrueStart MSRP
* Years 5-7: 25% of TrueStart MSRP
The document goes on to say that Toyota doesn't use the declining scale ("pro-rated warranty") that we usually see associated with battery warranties. Apparently the above program is what they mean by "simple two-tier price plan".
(Regarding the Walmart batteries, I've seen a lot of discussions boil down to whether they're made by Exide or Johnson Controls, with many saying the latter makes the more reliable battery).