Well, I'm not agreeing with or disputing the data, but you have to admit it seems counter intuitive.
After, what is a Seagate 3TB drive, if not simply 3 1TB platters stacked?
If you want to speculate what is "logical", the failure rates should escalate for each platter added. After all, with each extra platter comes an extra read/write head. Again, logic says the 4TB drives should suffer the highest failure, since they have the most moving parts, and ostensibly operate at the highest temp.
Given that I'm still not completely convinced "Back Blaze", is the alpha and omega source for drive reliability stats, they are starting to scare me away from Seagate. When I have my druthers, I buy WD Blacks. But some of the prices you see an Seagate drives are hard to ignore.
If you go in for checking Newegg reviews for HDDs, it starts to appear that every drive on the market sucks, with the exception of WD Velociraptors, Which I've started using using as the "C:/" drive in my most recent build.
(But remember kidz, "most recent", probably carries. an entirely different meaning for me, than for y'all).
FWIW, the WD "Caviar Blue", (160GB SATA 150), that came with my eMachines will be 10 years old in less than a month, and it's still spinning strong.