While I agree with the other posters, to me, the big problem with the Martial Arts Ability has been that it implicitly says that "everything that is not me is not Martial Arts." Which just seems wrong for a Kung Fu action game.
It's really not. Martial Arts as an Ability is saying "This is where systems bearing ancient tradition go; where your style adheres to strict in-style weaponry and where you may not proceed to learn pre-existing systems without a sifu, a technique scroll, etc. These are the fighting forms long since mastered and laid down, time-honored techniques such as Parallel Parking which are always the same, and which form standing systems of enlightenment based on tradition and adherence to form."
Also, rather than using the legalistic interpretation of a"martial art" as any
system of fighting, it is referring to the martial arts in the Asian tradition, as systems grounded in mysticism, transcendentalism, and zen ideals, not just a scientific catechism on dueling with a foil (fencing) or the system of breaking bones and winning rounds that is muay thai or to a lesser extent boxing. These last few examples fall under the modern day definition of martial arts, the legalistic definition. The one Exalted uses is the one that treats the martial arts as mystical, religious, spiritual systems as well as systems for fighting.
What a division of the Martial Arts Ability from other combat Abilities gives you is freedom from these ideals, not ignorance of them. Solar Melee Charms do not exist in any sort of a style, they are not universally on record or on tap; you can learn them as a matter of intuition. You don't need a mentor or a scroll and you are not limited to a form weapon (and a form weapon requires the correct stance* to use it 100% of the time, which means every regular attack you roll adheres to the slashing, stabbing, striking techniques of the style). Melee has none of these limitations, so that you can interpret it any way you want to. You can completely remove the mysticism component, the style and tradition component, and treat the techniques as something you came up with, and because the Charms do not adhere to form weapon rules nor do they rely on Form charms, you can fight with no stance or any stance, you can slash in any direction or in any way. You can be all forms, no form, one form. The non MA Charms are whatever you want them to look like and wherever you want them to come from. You can do Kain's Penta Thrust one second, toss away your spear, draw your sword and do Kenshin's final attack the next, and both are using IWA. You can't do that with a Martial Arts multiattack, because one weapon will work for it and the other will not.
*If you try to use snake swords, section staves, rope darts, nunchakus, and other style specific weaponry without using their associated style stances and accepted techniques of attack and defense you will die hilariously.