Hi Roger;
Your "complex" .epub is used to diagram a title page so you can see it no matter if the ereader is in portrait or landscape mode (you always will see the full page) without loosing quality (and also no matter the font size the user is employing). For other hand, the method in your "simple" .epub is to add .svg images to your ebook.
You could be wondering: why not using the second method for a title page? Well, do the try to use it, in order to get a page of 800x600 (or the size you want) and the resulting page would be heavier (because you'll be using "paths" for text). However, sometimes could be neccesary to use "paths" for text when you want to "mimic" a copyrighted font. Of that way you could have the font you wish (for the title page) and the same time you won't be using a registered font.
But in principle, you should see both methods as complementary and not excluyent
