Pretty sure that is how it works on the Nikon DSLR's too.
Same in the Pentax world, too.
I turned mine off at some point in WDW after getting tired of waiting a while after some of my longer tripod shots. Never turned it back on, I see little difference - as long as the original shots were at a fairly low ISO (as they would be, if I'm taking an exposure that long), I see no noise issues.
As for point-n-shoots like the S3, I believe that all do basic noise filtering, different levels for different ISOs, and you're unlikely to be able to change any settings - it just does it. If you have one of the more advanced PnSs that can output RAWs, you can bypass that noise reduction and do your own as part of your raw conversion workflow; and there's a very good chance that you can get better results than the camera can.
Even with RAWs, you're still getting some filtering. This happens with DSLRs, for example, certain Nikon and Pentax cameras use pretty much identical sensors. From what I've read, Nikon tunes their to give you slightly more noise reduction at the expense of a little fine detail, while Pentax gives you a touch more noise but a little more detail, too. The differences are very slight and probably only noticable to pixel-peepers poring over lab tests, but there are differences.
And with the JPGs from PnS cameras, it can be all over the map. We'll probably see more and more aggressive noise filtering as high ISOs are now on the "must have" list for cheaper cameras. A camera with 8+ mp and a 1/2.5" sensor and ISO 3200 has to do a lot of noise reduction to give you a remotely usable photo, and by and large, more noise reduction = less detail. Pick your poison, as they say.
