How is it any more of a "disposable gadget" than the previous generation which has all the same soldered components but the RAM, exactly?

My current machine got its RAM upgraded once, the day I bought it, and will never see an other RAM upgrade in its life because I'm at the chipset's capacity. It's in the exact same position as the new mbp. Has it suddenly become a "disposable computer gadget" where it was an "expensive professional tool" between the moment I received it and the moment I put the new ram sticks in? Even though I hadn't even booted it up at that point, and it's my day-to-day workhorse now?

According to the post you can't replace the drive or the battery either.

The post says nothing about drive or battery, the iFixit teardown does confirm the battery can't be replaced (it's now glued in — where the old one was screwed to the case — the teardown guys didn't dare removing it after trying a bit) so there's that.

On the other hand, the SSD is most definitely replaceable, it's the same system as in the Macbook Air (though apparently not the exact same drive): http://www.ifixit.com/Teardown/MacBook-Pro-with-Retina-Displ...