Flash question

Hi,

I have what might be a very basic question ...

My new 60D just arrived (hooray!), and I'm using Speedlite 430.  I think the flash sync speed of this camera is 1/200s (maybe 1/250s -- I can look it up), which is the fastest shutter speed that can be used with the flash.

When in Program mode, the camera chooses 1/60s and f/4 as the exposure settings by default.

Why can't I use the dial to change to another equivalent exposure, like I can do when there's no flash on the camera?

I'd like to use a faster shutter speed (and maybe even a smaller aperture setting).  If I go to Tv and set the shutter speed to 1/200s, the aperture flashes at f/4 (the widest aperture on my lens).  Or, if I go to M and set the exposure to 1/200s and f/5.0 -- assuming that's the exposure I want, the exposure level indicator flashes at -2.  In both cases, the camera is telling me my picture is going to be way underexposed.

When I take the photo, the exposure/histogram looks fine.  Presumably, the flash compensates for the exposure setting (?).  But my question is why doesn't the camera let me know that the exposure is fine?  Or, is there something it's telling me that I'm not getting?

Thanks.