The minor point that your comparison is missing is that if, overnight, your baker has increased the price of the baguette from £0.80 to £1.50, while the baguette is becoming 10% smaller, (s)he will fully expect a lot of outraged comments from his/her customers. (S)he will be only too glad to be able to explain why (s)he had to change the baguette prices, discuss the changes with customers, and to give them his/her view on why the customers would still, in his/her mind, enjoy good value for money bread if they keep buying his/her baguette. As for the tone of the negative comments, given the circumstances, the baker will most certainly take the rough with the smooth because (s)he will have expected both. Your baker has certainly got his/her reasons to have nearly doubled the baguette price and aligned it with the price of the pain de campagne, may indeed be right to do so from his/her point of view, but no baker I know would be silly enough not to expect the very unhappy reactions.

And of course, the baker will also presumably feel gratified (but not surprised) that the people who buy pain de campagne for £1.50 will feel happy with the changes, especially if they have been told that their pain de campagne is now 10% bigger for the same price. What is changing in your bakery is creating some winners and some losers, and your baker won't expect them to react in the same way, and knows perfectly well that if the decisions had been reversed (no change in bread prices and a pain de campagne that became 10% smaller while the baguette was becoming 10% larger), the reactions would have been symmetric too, nothing unusual there.