Saul Hansell wrote a good, "hold your horses, there"-type article in the New York Times on the apparent all-out war between Netflix and Apple's online movie rental offerings. In the article he explains that, while both are technically in the online movie rental business, they actually cater to different markets: Netflix concentrates on having a large collection of older movies as an add-on to its DVD rental business while Apple is going after the latest releases and is positioning itself as an alternative to DVD rentals. And, though there is an overlap, for the time being both companies should be happy in their own niches.
Of course, there's also the issue that Netflix's service doesn't work on the Mac while iTune's service works on any OS as well as on Apple's portable media devices (Apple TV, iPod, etc.). Again, that's not too much of an issue since they are catering to different markets. People who rent DVDs are probably not the type who'd want to watch a movie on their tiny iPod screens. Of course, Netflix is still missing out on the small proportion of users who own only a Mac, but I guess adding a Mac-compatible offering of an already add-on service isn't all that high in its list of priorities.