Just to be nice and actually answer this person's question rather than just downvoting them:
The distinction, as I understand it, is that labeling it an "open letter" tells us that one entity (Readability) intends not just to publish a given letter for all to read, but also make clear that it is directed at a second entity (in this case, Apple), in the same way as if Readability had sent it directly TO Apple.
It is also often hoped that such an open letter might elicit a public response.
The distinction, as I understand it, is that labeling it an "open letter" tells us that one entity (Readability) intends not just to publish a given letter for all to read, but also make clear that it is directed at a second entity (in this case, Apple), in the same way as if Readability had sent it directly TO Apple.
It is also often hoped that such an open letter might elicit a public response.