There have obviously been an awful lot of responses to Steve Jobs’s open letter; I’m not really interested in debating Apple’s “all or nothing” position on DRM (refusing to sell some songs DRM-free on the iTunes Store, even when their publishers would want them to, because it would be confusing or something), but this article makes a good point (emphasis mine):

In the timeframe that FairPlay was [compromised] or circumvented at least four times, Windows Media DRM was verifiably cracked once that I’m aware of, last August. Microsoft patched the August hack in a few days’ time, and had the patch out to licensees in that same timeframe. Another "crack" could purportedly strip DRM from videos that you already purchased, but it was never fully verified, and Microsoft released a general Windows Media update that appeared to stop discussion of the matter. […]

As Jon Johansen points out, the [security through obscurity] angle is "not a valid argument in this context since Steve was claiming that sharing DRM secrets with lots of licensees will inevitably lead to one of those licensees leaking secrets. As far as I know, none of the MS DRM breaches have been due to industry insiders leaking secrets."