It's not a "latest" thing -- the Mac Mini has always had an internal power adapter. Whether or not that's worth the thermal trade-off is a different question.
I still have a 2006 Mac Mini, and its power brick is external. The size of the computer suggests it was built around the optical drive, while the newer Mac Minis are visibly wider than a CD. http://lowendmac.com/2006/mac-mini-early-2006/