Is the difference in the forms in the philosophies and how agressive each one is?
I'd say you hit the nail on the head right there, at least from my point of view.
These Forms affect
how attacks are utilized, as well as overall tactics. The way I look at it, Shii-Cho teaches you the basic strikes, which you take and adapt to the other Forms.
Example:
Padawan A learns Shii-Cho, and decides he wants an aggressive saber form. Picking Djem So, he learns to empower his strikes through the Force and turn attacks back against his opponent. He still uses the same types of cuts and movements, but subtly modifies them for his own uses (more windup for stronger attacks, for instance).
Padawan B learns Shii-Cho, but decides he wants more control in his form. He picks Makashi, and modifies the techniques he learns in Shii-Cho to be smaller and more single-handed, for more precision.
If you want to truly learn Juyo (or Vaapad) you'll need to learn to channel your emotions for fuel. It's a difficult ability for many, but can be very effective for those who master it.