Question about the design choices in "Grouping and dividing content"

Question about the design choices in "Grouping and dividing content"

This is a more "why did you do it that way" question versus "how do you do it." I was looking over the examples here ( http://demos.jquerymobile.com/1.4.0/body-bar-classes/) and I was curious why "Heading attached to section - custom rounded corners" was built to require custom css? Is there any reason why this can't be supported in the default CSS? Since *anything* is possible with custom css, why is this included in the first place?