I stand corrected, perhaps AVs can detect future malware. BUT (and this is a big but) the effectiveness of heuristic analysis is still fairly low. Heuristic analysis is basically a best guess effort of identifying new malware based on past experiences. With guessing there also comes the increase of false positives. Although it is possible, the usefulness is questionable. This quote is taken form the link you provided.
"Although heuristic analysis is capable of detecting many previously-unknown viruses and new variants of current viruses, the effectiveness is fairly low regarding accuracy and the number of false positives. This is because computer viruses, just like biological viruses, are constantly changing and evolving. Since heuristic analysis mostly operates on the basis of past experience (by comparing the suspicious file to the code and functions of known viruses), it is likely to miss new viruses that contain previously unknown code or methods of operation not found in any known viruses. Fortunately, heuristic analysis is also evolving along with the viruses. As new viruses are discovered using alternative methods of detection, information about them are added to the heuristic analysis engine, thereby providing it the means to detect any new viruses based on the previously-unknown code."
In the case for android, heuristic analysis doesn't really come into play considering there's not much of a history for it to learn and discover from. The droiddream exploit is one of the first root exploit we seen for android. I doubt any AVs could have caught this ahead of time.
