Raspberry Pi is actively preventing enthusiasts from upgrading soldered memory to a larger configuration even when the replacement chip is technically compatible. The company says the restriction is intended to discourage unofficial high-capacity resales.
They already have authorized resellers, who they link to on their website. This problem would only come from unauthorized resellers, who would not qualify for warranty service. It might not help software support requests, but I don’t know how much support they offer for software since I don’t think they’re supplied with any. Anything hardware they should be asking for a receipt from an authorized reseller, and if the customer can’t provide it then it’s not covered by the warranty. And even if the customer can provide a receipt from an authorized reseller in their name, if it comes in for repair and has the wrong RAM then it’s not a warranty repair anyway (although I’m guessing for something this inexpensive they don’t repair individual units, they probably just send a replacement, so the counterfeit parts might not get noticed).
One consideration is that the community support would not like the fallout of shady 3rd party manufacturers/resellers putting out faulty hardware either.