Re: In an ideal world...
It's true that DRM will not prevent pirate copies from appearing 10 seconds after the content goes live, but the people who are paying still get a gimped service.
Gimped in what manner?
DRM has not been practical for preventing piracy. They use it to control average users. So far, DRM has been especially effective in DVD, BluRay, HDCP, Apple iTunes, and Amazon Kindle. I don't care about video games, but it's there, too.
In DVD and BluRay, DRM prevents you from buying a disc in one region and playing it in an average disc player in another region. The media companies want to use differential pricing and staggered release dates to maximize revenue. Sometimes they decide that a region isn't worth the cost of releasing a product. Tough beans for you if they decide never to release a disc in your region. Also, DRM prevents you from skipping ads and propaganda about fictional laws that they insert at the beginning of movies.
HDCP theoretically prevents you from copying movies as you're playing them. In practice, the HD stream is so big that, even though the HDCP master key has been leaked, nobody bothers using it to pirate. You get better speed and quality from breaking the AACS encryption on the BluRay. Instead, HDCP ensures that you're using properly restricted media players and properly restricted output devices to play videos exactly the way they're intended to be played. But there is some minor flaw that makes the DRM in your fancy-expensive device not operate properly with the DRM in your other device? Too bad, so sad.
Apple and Amazon use DRM to make sure that, if you buy any content for your fancy gadget, then you're trapped with that brand of fancy gadget for the rest of your content's life. Apple does it to make their line of fancy gadgets more attractive to buy, making more money on hardware sales than music sales, though now also making a lot of money in the App Store. Amazon is in the low-margin high-volume market, and wants you sticking around for them to shove ads in your face. Also, Amazon uses DRM to remote-delete content from fancy gadgets, including, fittingly, copies of George Orwell's 1984.
DRM has not yet been effective at preventing piracy, but it has been great at causing problems for people who want to use content legally.