The difference is that mainstats on tanks are only worth 0.45x as much when calculating actual attack power, dropping that to about 4 Attack power, at the cost of 1500 hp.
The difference here, and what makes these BiS theorycrafting threads so ridiculous, is that you can actually get use out of 1500 more hp by eating busters in out of tank stance, or saving your healers GCDs over time, instead of 0.3% more DPS(assuming 1300+ Attack Power at full i270), which will not even be detectable on a parser due to crit variance.
HP does something, fractional percentage DPS increases do not.
