The short answer is that there is a kind of Markdown support for tables in Markdown Extra - I'm surprised it hasn't been mentioned in this thread yet (according to Ctrl + F search, at any rate), although we have had GitHub-flavoured Markdown mentioned.
This has been implemented for a long time, and the "syntax" is pretty well-known. One thinks it would be a simple and effective enhancement for SO/SE. As a bonus, a move to Markdown Extra would bring definition lists, too -- and even footnotes (hurrah!).1 ;)
1 SO might not need 'em, but SE most definitely does! In addition, see now the 58-times UV'ed (as of this writing) "Time to fork markdown?", which explicitly draws attention to footnote and table support.
