You're right. I was thrown off by the message higher in this thread that called them Torx screws. These are not Torx, they're pentalobes, and yeah, it's a non-standard by any reasonable measure.

That said, I'm still not agreeing with all this carping. You buy a product that's not advertised as having user-serviceable parts inside, then complain it's hard to service. I don't see folks complaining that the inside of their Android phone or Dyson vacuum are hard to hack, and that's what the iMac is equivalent to - it's an appliance. You trade away the flexibility of a desktop form factor for the coolness of the all-in-one.