According to Adams Media Research, the growth in DVD sales is reaching a peak. In short, with the increased usage of on-demand and downloadable content, it's predicted that DVD sales are reaching a peak and will begin to wane in sales. Ultimately it happens with all media, but with the struggle of HDDVD and Blu-Ray it may have a more marked impact.

”DVD sales growth is slowing, according to several recent reports. A study released by Adams Media Research in October forecast DVD sales of about $17.3 billion this year, a 12 percent rise from 2004. Adams forecast a 9 percent rise to $18.9 billion in 2006.”
With technologies like HDTV being readily available and 4.7GB just not cutting it anymore, modern DVDs are reaching a point where their usefulness may be surpassed by online content or larger discs.