Hmm. They didn't just switch to 25nm NAND, that happened in Dec 2010, as reported in an article here on MyCE.
Also, while the laws of physics mean that 25nm has fewer write cycles than 34nm NAND, life expectancy is still 5 years (the same as 34nm) and the warranty is still 3 years.
Also the quality of the NAND hasn't been taken into consideration.
You can have 34nm NAND that is only good for 3700 P/E cycles, and 25nm NAND that is good for 4000+ cycles, or eMLC that is good for 30,000 cycles.
Having said that, it would have been easier for consumers if the 25nm model numbers had been changed.
The 100GB and above 25nm NAND models (because of the NAND density) speeds are almost identical, as the higher density NAND can access all channels on the SandForce controller.