Is it true that you are unable to center tables in EPUP2?
I believe your question is not about the EPUB 2 specification but about behavior of common EPUB 2 Reading Systems such as Adobe Digital Editions. It does seem like there are known problems here, but perhaps as well some workarounds. See e.g. http://infogridpacific.typepad.com/using_epub/2010/02/epub-best-practices-2010.html
EPUB 3 defines a much more expansive CSS Profile (a superset of CSS 2.1) and in practice will often be implemented using a Web browser engine. So this problem should recede as EPUB 3 based Reading Systems roll out during 2012. Since Apple iBooks is already based on the WebKit browser engine I would suspect it is not a problem for iBooks right now (even though officially iBooks doesn't yet support EPUB 3).