@toxaris --- iBooks uses webkit as a rendering engine. It gives really good and predictable results. Other ePub readers also use browser as their underlying browsing engines.
Speaking of specs, according to the official EPUB specs, version 2 in many cases just picks up the official CSS2 specs! In fact, for margin-left: auto applied to DIVs and tables, the official specs say that it should behave just like a browser.
Here read it for yourself:
That document tells us that for margin-left the EPUB specs follow CCS2 section 8.3. Those specs tell us that for DIVs and tables (block-level, non-replaced elements in normal flow), margin-left:auto, and margin-right:auto should center the object horizontally:
So there you go. ADE sucks. The only reason I'm using it is because of the DRM.