Well, `'html'` is just the default value for `$format`. If you want it unescaped (for ajax requests for instance) you can pass `'text'`.
Sure, we could remove the `h()` calls inside the Display methods, and enclose the method call within `h()`, but since this `h` should be written almost everywhere this may lead to errors since developers have to remember to call h.
Furthermore, we have that these method are called `get…Display…`, so IMHO it's quite clear that we're willing an escaped value to be used for display reasons, and since display in our case means 99% of times we have to generate html the default value for `$format` is `'html'`