Actually, *many* of the compacts can do what you ask though they don't all do it w/ the same degree of capability.
On most respectable compacts that don't allow you to manually adjust flash exposure, you can usually put the flash into slow sync mode. That will do more or less what you want though you'll probably need to have super-steady hands or a tripod (or something steady to brace against).
As for manually adjusting flash exposure, which is what I assume you're asking re: that Panny cam, 1 EV = 1 stop of light exposure in general. And negative EV compensation would translate to exposing the subject at reduced light level (or brightness of the image) relative to the camera's exposure meter choice -- camera meters are usually set to aim for an average exposure of middle gray (or something like that), which could be as much as 2/3 to 1 EV too dark for a fair skin, blond haired caucasian for instance. 1 additional stop of light exposure (or +1 EV) is equivalent to the amount of additional light needed to expose a subject at 2x the shutter speed or "half" the aperture (very loosely speaking) or 1/2 the ISO setting. RE: aperture, the f-stop settings actually progress in steps of roughly 1.4x (or square root of 2 to be more precise) the previous value for each EV or something like this: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, etc.
What you may actually want for flash exposure compensation will vary depending on exactly what results you're trying to achieve. And it doesn't really replace the need to understand how to shoot w/ "slow sync flash" when the ambient light is not the sun or similar.
Basically, slow sync flash just means you expose w/ settings appropriate for the ambient light w/ "fill flash" added (more or less) for the subject (or parts of the scene) that needs the fill light.
Hope that helps...
_Man_
