Re: Aikido: The learning of natural movement
Mike already told you the reason for striking the mat. In addition to that it does condition the extremities as well as teach you a fundamental basic in the act of timing. If I was to be in situations where I had to be falling outside and needed to protect myself then I most certainly would want to have the added protection of "deaden arms". However, since we don't train to those kinds of extremes I don't think you have to worry about any supposed arm damage.
Either way...the way of the Yoshinkan is to strike which I have been doing for years with no such complications that you speak of. I can take ukemi from senior practitioners without missing a beat because there or very specific core elements to the art of falling. If you have to ask what the meaning is behind striking the mat pretty much says what your understanding is. If you further more think that striking the mat is the only way to do it and the fall then becomes to "heavy" and you don't adjust/account for that says a lot as well.
Would I slap on a very "heavy" fall, most likely not. Do I train to be able to fall correctly with specific drills...why yes I do. It is part of the basic curriculum of the Yoshinkan and is taught as part of kihon training. It is just as vital as learning the basic movements of offense.