It seems to me like a lot of basis for Riolu/Lucario's abilities are based on that of spiritual monks, and the use of Aura, or qi, to produce various effects. Probably the best example of this is in the move Force Palm (Which Riolu learns very quickly) and the move Aura Sphere, which is a nonphysical Fighting move. Riolu/Lucario are stated to be able to read aura in living beings and predict their movements. Given Lucario's design, one can assume that it is, or can be, a very skilled martial artist, which means that realistically speaking it could read the weak points of its opponents and strike with aura power.
That being said, Lucario seems to have a penchant for being very spiritual, and can focus that spirit in training. The games do not reflect this at all as a rule, but given the right kind of training, Lucario could be a very, VERY dangerous Pokemon to use. I can easily see a Lucario completely dominating a more powerful creature than itself by reading its weaknesses and striking hard. The anime has already shown some of Lucario's poential skill in the movie showcasing him.
What are your thoughts on this matter?