What I like about martial adepts (and warblades by extension).

More efficient use of the action economy. A higher lv wizard can move, fire off a spell as a standard action, cast another swift action spell, and still use an immediate action in response to his opponent, such as abrupt jaunt or duelward.

Fighters move and attack. That's pretty much it.

Warblades can move, initiate a standard-action strike for respectable damage, mix a swift-action boost into this somewhere (say lightning recovery to reroll that missed hit) and still perform a counter (eg: moment of precise mind vs mind flayer's mindblast) when it is not his turn.

In the end, it boils down to options available.