In the grand scheme of things, this is trivial, but it's a bit of a "chink in the armor" of Amazon Prime's chief shtick: fast free shipping (after the membership fee, of course). I received this from them this morning:
For comparison, Walmart+ gives free delivery (and not just on groceries) from local stores (at in-store walk-in prices) for orders over $35 and with a $2.99 fee below that.
Like I said, this is not a big deal IMHO (I've never thought unlimited free shipping via paid membership was a sustainable model anyway), but between this and Amazon announcing Amazon Smile's impending demise last week it's clear they're tightening the belt in important ways -- quietly reducing their philanthropy while saving face, and beginning the slow but inevitable process of shifting shipping and transit fees back onto the consumer again.
If I were to hazard a guess, I'd say the next "upcoming change to keep prices low" will be "throttling" -- Netflix style -- capping the number of free shipping purchases you can make in a given period (7-day sliding window, one calendar week/month, X times per year, etc.) before incurring regular shipping fees or slower shipping (or both).
I have to say I love/hate the doublespeak in the message. "This service fee will help keep prices low." If you're increasing fees but not lowering prices (the language is careful to say "keep prices low," not "help reduce prices further"), you're raising your prices. Such scummy slight-of-hand. Sad that so many people fall for it.