The idea seems to be that "raw" HTML and CSS are easy to misuse as well as potentially making a page more difficult to edit. However, Wiki markup, such as the example for alphabetized lists, is actually a layer of abstraction which in turn renders (somewhat more complex) HTML and CSS automatically. I think Wikitree doesn't want to needlessly constrain against using an available Wiki markup feature just because they did not provide an example if its use. However, if some feature becomes problematic in the future they reserve the right to advise against it.