I am talking only about common block for IP numbers, not users. Moreover, I am strongly against blocking user's account on one project for things he has done on another project. So please do not make off topic and discuss what NPOV is and what it is not, because we are on technical list.
With IP numbers the situation is completely different. Common behaviour of occasional vandals on English Wikipedia is switching to (for example) Wikibooks immediately after having IP blocked and going on with vandalising random pages. This is really hard to catch by sysops and could be very easily stopped by automated propagating IP number block to all available Wikimedia projects. Whether it would be done by creating common database (similar to Commons) or by a bot similar to CommonsTicker - it's irrelevant for administrators of projects suffering from vandals coming directly from Wikipedia. In most cases 2-hour block restricted to anonymous users is just enough to stop vandal.