CSS Sprites (or lack thereof)

I have always wondered why Storyline output contains individual images during publish for html5 when it could include a CSS sprite mechanism to reduce the number of HTTP requests (the same way it has been done for some player buttons - see controls.png) .

Example : Say we have a slide containing a single picture with 3 states. In the mobile folder, I'd have 3 different png and swf files for each of the 3 states of that 1 picture. Why not generate a css sprite during publish to have 1 HTTP request instead of 3 for that picture?

To make this even more relevant, why not create a single css sprite for all elements in every slide to have an even further reduction in HTTP requests (since it is likely there are more than just one element in every slide).

Was that a design decision or would something like this have caused other limitations in HTML5?

Cheers,
Alex