Are DVD rentals on the way out?

According to this article in Slate.com, Wal-Mart is almost single-handedly keeping the movie DVD market alive by keeping open one very important window of opportunity.

[The studios] have created an artificial barrier called the video window, which prevents cable operators and TV stations from showing movies at the same time as their release on DVD. In the case of pay-per-view, the window is 45 days; with subscription cable such as HBO, it is at least four months. ...

What has prevented the studios from closing the video window is simple: Wal-Mart. The company, which is the single biggest seller of DVDs, has made it clear that it does not want to compete with home delivery.