He seems to be trying his best to find flaws in the study, but his own logic is pretty poor. For instance.
"I’ve noted that we just found that the Seagate 1.5 TB drives are about 8 years old since release, for the failure rate, but the average age of the Seagate drives in use are 1.4 years old. Averages are pretty useless statistic, and if Seagate drives are so bad then why buy so many new drives?"
If the company began rolling out Seagates for 3 years at 5k a year and stopped after three years because of the high failure rate, moving on to Hitachi and such, then the average age even over 8 years could very well be only 1.4 years. Because, let's face it, when it's your ass on the line and you see a particular type of drive putting your servers into a precarious state, you might start migrating away as fast as you can.
Those Seagate drives still running are probably either running in very low IO servers or very low-risk servers (clustered or such), but in such few quantities that their continued lifespans are not increasing the overall average much. The remainder could be shelved to avoid the risk of failing in a critical system and while they are listed in the total number of drives purchased, their age might not be included in the average presented.