Here' s a couple shots of the motion/gravity-sensing device that's in the Sixaxis and the DualShock 3. It's pretty dang small. It's weird to think that Sony actually claimed that rumble would throw off the functionality of this tiny device, and that's the reason the company omitted rumble in the original Sixaxis. Still, would you rather have motion controls or vibration? An easy choice, but at least with the Dual Shock 3 we get both.
That little chip inside the Sixaxis (attached to the centre of the board) is apparently what gives the controller the capability to recognise motion-based gestures.
An upclose view of the Sixaxis motion-sensing device. It's about the size of a fingernail.
Now, for comparison, here's the PS2 DualShock 2 controller. Notice how different the inside is, with the exception of the rumble packs, which have a surprisingly similar structure.
Here's a look inside the original PS2 DualShock 2 controller. We've come a long way, huh? Notice the rumble packs in the side palm areas. A little different than the Dual Shock 3, but the same general design.
Inside the DualShock 3.
Here's a closer look at the DualShock 2 right side rumble pack.
Again, here's the right side rumble pack in the DualShock 3.