The contacts are gold, which definitely doesn't oxidize...

This looks like gold plated to you?

When will people learn, don't trust everything you're told, check for yourself.

The solder doesn't really add any contact surface area...

Plase take a look at the two, and tell me the contact area is the same. Solder wire is 60% tin, 40% lead (Sn60Pb40). They are both soft metals at room temperature, thus, they displace when pressure is applied on them, like from a needle for example, and they make a nice bed for the needle to lay in, maximizing surface area.

...and even if it did, it makes no difference for digital signals...

Oh, now I just know you know nothing about electronics.

"Better conductivity" doesn't improve digital sigs either.

You do know that it's not just I/O data that goes through those pins, right? Look at some of the buses on the PCB, not all of them are the tiny, there are a few thay are quite thick. You know what they are? They're the magnetic coil control pins, the thing that makes the heads move accross the surface of the disk... you know, the thing that fails when there's a head crash. It takes power to move the head, thus, it's not just a signal now, is it.

I can't confirm the last paragraph, but HDD manufacturers could just move the PCB closer to the chassis and/or make the contacts' springs a bit stiffer to achieve the exact same thing, which is slightly more pressure between the contacts. That's literally all you're getting here.

Look at the doodle again, and you'll see I'm right.

I didn't come up with this idea on my own, as I said, I looked at how things were done in the past, when drives were really good. Everyone soldered the contacts for the pins back in the day, and then, they just stopped. WD were the first, others followed.