Yes, I honestly believe DRM does a lot to prevent piracy. Will it prevent the techno-weenies and the dedicated types? No. But it does prevent casual piracy. Ultimately, that's all that's needed. To raise the barrier to piracy beyond simply copying the file over to your buddy's iPad or USB drive. All it takes is making it that little bit more inconvenient than buying the thing legitimately and most people won't pirate.
As for the 10% of dedicated pirates that will never be stopped? Meh, cost of doing business.