They used to, in Australia at least. I can't remember if it came with my iBook G4 or one of the Intels soon afterward, but out of the box I got both a two-prong stub that attaches directly to the brick and a ~1.5m cable that goes to a three-prong plug. I sold the original laptop long ago but kept the old grounded cable all the way up to my current work MBP. Personally the buzzing drives me nuts.

The first time I noticed it I was a bit worried about it all. I had a volt stick from work (a safety device to identify live wiring) and surprisingly it illuminated when I brought it near the metal chassis of my macbook. Some further tests with an oscilloscope showed that it was floating a good couple of hundred volts, but the capacitance was so low that the energy payload was never going to do any harm to a human. I don't care, I still just ground the thing.