The challenge with the original wiki implementations using "wiki markup" are that it was hard to get non-engineering members of a team to use them (or at least contribute). WYSIWYG editing in the browser window changes this for the better.

The second key defect early wikis shared was a lack of contention management. When you are working against a deadline you need a contention management (e.g. file locking) scheme so that "he who saves last saves best" is avoided. I have seen this cause much unhappiness for projects when a wiki is used that allows "forks" in the history with two or three people editing the same base version with different results.