That is incorrect.
Items weighing less than 100g and selling for under £10 will be exempt from Simple Delivery.
So, a lot of private sellers will still be using stamps to post their light, low cost items.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)