Did you even read it, or just look at the chart? It clearly talks about the different carries as well.
"One interesting finding with 3G data was that while their Verizon 4S unit ran for the same time as the AT&T model (~ 5 hours and 54 minutes), they found the Sprint model to lag at 5 hours and 23 minutes. Comparisons across mobile providers may not be completely fair due to differences in signal strength which could impact battery life.
In voice calls, they found the AT&T iPhone 4 and AT&T iPhone 4S to have comparable times of around 7 hours and 6-16 minutes. The Verizon 4S model, however, showed a surprising 8 hours and 27 minutes, while the Sprint 4S again lagged at 6 hours and 27 minutes. iLounge notes that the Verizon model may have shown 4 bars more often than the other two. "