While the use of liquids to absorb shock has been suggested before, Sony's engineers are confident that their version is more effective and will be able to absorb more shock.
Excerpt from Techworld:
"The new scheme proposes that the fluid-filled inner skin will also contain 'biasing units' to keep the electronics central, and a system of irises that adjust their resistance to liquid flow according to the force of impact.
... as the walls converge under pressure, the protrusions come closer together and provide increased resistance to the flow of fluid... absorbing more shock."
It took a few more reads than I normally do (don't you just love patent talk), but it appears to me that Sony basically put some carefully crafted bits together into the liquid/gel layer. These bits help reduce the movement of the liquid/gel, resulting in a much higher shock tolerance.
If you're still confused, you can check out Andy Moon's TechRepublic blog post Not everyone can (or wants to) be a geek as therapy.
For the rest of us, let's discuss this topic.