Adobe have said that they will develop version 4.0 for Mac but that they've no timetable at the moment. Remember that iPhoto competes in a small way with Elements and in a larger way with Album, which obviously isn't being developed. iMovie makes it difficult to sell Premiere Elements.
Adobe had no interest in the market, so Apple did something. Since Apple did something, Adobe has reduced interest in the Mac market.
A bit off-topic but did anyone else notice that Corel introduced Painter Essentials, which is pretty much exactly what Fractal Design Dabbler used to be? It certainly complements Photoshop Elements.