Not so unknown. Early PDFs of the rulebooks made it into various illegal distribution channels. If you can't control what happens with the material after you release it, then you can't release it and expect to profit from it. They didn't.
If you're using and paying for DDI then you're essentially getting what was promised, AND they're still making money from it. I use DDI too but I still prefer to have real books, however flawed.
Pretty sure there are 'late' PDF's of the rulebooks in various illegal distribution channels too... even after they stopped. I'm guessing they are hoping people will pay for DDI for errata, then?