There being valid reasons to solder RAM doesn't preclude being annoyed at Apple for charging 3x the market rate to upgrade it with them, I suppose. It'd be a lot less controversial if that were the case IMO.
I don’t think anyone is saying you can’t question their pricing. My disagreement is solely with the very confident assertion that this is done to prevent upgrades with no awareness of all of the other reasons.
I wouldn't be surprised. It was common back then to hear on forums to never waste money speccing up the ram on macs, since you can upgrade it yourself for half the price with sticks from crucial. It was always a $200 upgrade even when you were just getting another 4gb of DDR3.