As a frequent "small purchase" buyer getting stuff from across an array of sellers I agree that some postage costs have made me cancel some potential buying. Just like exchange rates, postage can be a big decider on buy/not buy decisions.
I think if you lock yourself into a particular range of miniatures you may find yourself in an "all in or all out" dilemma. Sometimes (like my soldados de cuera in 25 mm) there
only is one source (thank you Dayton Painting consortium for reasonable costs and great customer service) for what you are looking for. More often our personal comfort zones ("too cartoony," "too tall," "Too chunky,") narrow our options down. That is not a criticism but a description of our practices...
Finally, I think it is a market driven individual decision by the seller to risk the turn off or to optimize different aspects of the business that drives
their decision on how to ship. I doubt any company plans to buy out Microsoft or Apple on their earnings selling hobby items.
Greed on steroids is seldom a significant temptation in miniatures pricing IMO.
Gracias,
Glenn
Edit: on the surface and second hand, yes that price for shipping decals would make me "why" to the seller. There may be an unusual circumstance I, as the buyer, may not be aware of in something like that.