Hmm you are right in the point that the format of the spip files is not as simple as it could be (but simple enough I think - and as simple as I like it ;-).
(You don't have to type much even if you write the presentation in the night before. Just copy the spip file from another, change chapter and subchapter (and perhaps the picture) and the data and thats it. Perhaps I think HTML is simple because I use it much. I wanted to use HTML in the data block because I wanted to have the freedom to use any HTML command I like in there. It's allways a question on what you want from a tool.)
But the "Simple" in SPIP means that the presentations are only simple compaired with Power Point presentations with movements, sound and what else.