Mainly the video playback support by Zen.

Creative Zen - WMV9, MPEG-1, MPEG-2, MPEG4-SP including DivX 4 & 5, XviD, Motion-JPEG

Apple IPod - H.264-LC (1.5Mbps peak bitrate) at maximum of 640x40 pixels, or H.264-BP (768kbps peak bitrate) at a maximum of 320x240 pixels, or MPEG-4 SP (2.5Mbps peak bitrate at maximum of 640x480 pixels), each at 30fps with AAC-LC audio up to 160kbps.

Microsoft Zune- WMV Main Profile (1.5Mbps peak bitrate) or WMV Simple Profile (736Kbps peak bitrate), each at a maximum of 320x240 pixels and 30fps, with WMA audio (stereo) at 192kbps max

This comparison shows,the other two products than Zen needs additional video codecs or conversion for playing the most common downloaded Divx files.If you look at the torrent movies,all are coming with MPEG2/Divx format and i think Zen is the only player works with it without a conversion..!