Again, unlike commercial software, Linux is developed in a completely open manner. Anyone and everyone can subscribe to the master developers mailing list or one of the several more project-specific lists that abound. However, the posts that appear on these lists are no more official or set in stone than what you might hear during a conversation around a water-cooler at a more traditional place of employment. But just because something is uttered by a developer on the mailing list doesn't mean it constitutes an official word from the development team or even an idea that won't be thrown out a week later because it proved impractical. The bottom line is that every Open Source project that ever announced dates or feature sets have tended to be wrong.
Commercial software seems to be bitten by the same bug.
Release dates and feature lists are often born in the marketing department where the laws of reality are not the same as in normal space. Things that seem easy to implement are often complex. Things that seem useful often prove to be useless in the field. Because Linux is developed by programmers without pressure from marketing folks or a bottom-line, it is less prone to being rushed just to get it out the door. Linux 2.4 will be released when it is completed and not a day sooner.