One of the recent iOS updates by Apple was met with public outcry as iPhones were draining battery much quicker than before the update was applied. An update to that update seems to have the same problem. Now Google decided to jump on the same bandwagon — a recent update in the form of Android 4.0 (aka ICS or Ice Cream Sandwich) does the same — sucks the battery empty on Nexus line of phones (Nexus S and Galaxy Nexus to be precise). Google decided to hold off the update until the source of this drain is inspected and resolved.
In this article you can read about speculations as to why faulty updates are hitting the market — I mean c'mon Google and Apple — you can afford beta testers!