> Compare this to Webkit - where there is no requirement to share code, but you have a number of companies that have setup very successful developer communities

> Compare this to Webkit - where there is no requirement to share code, but you have a number of companies that have setup very successful developer communities around the code base... Huh? Webkit was based on an open source project (KHTML under the LGPL) and there is a requirement that the code be shared. Also Apple basically did the same thing as Amazon did here at first: they just dropped huge tarballs on the developers with no comments. In fact, attempting to merge Apple's changes in without comments was so divisive that the forks split, and only years later did Apple open up to an extent with WebKit that it became a proper collaborative effort. As for whether or not it's useful in practice ... note that I am one of the authors of one of the things they released, and my first reaction was to run a diff against the original to see if they'd made any interesting changes (they haven't).