The math is not so simple as that, because these devices waste some battery while on stand-by. So if you don't turn them completely off (which is not usual, due to the painful amount of time it takes to start-up).
With my nook (first edition), I've found that I can read between 10 to 14 days of aprox. 1 hour a day (about 12 hours of reading), but I can also use it for 3 days of 8 hours a day (about 24 hours of reading) -only feasable on holidays, obviously-. All of this with wireless off, and none of it an exact measurement, just what I've experienced.
So yes, measuring battery life is hard, it depends a lot on the use you give the device. However, it annoys me that it wastes so much battery on keeping it on stand-by. Maybe they've worked on that for the nook 2, and that's why they are parading their 2 months estimate. Because, with the old nook, it's not true that you can double the amount of days the battery lasts if you halve the amount of hours you read.