The downside comes when there’s coupling amongst applications, as there is increasingly with mashups and aggregations of web services. When an interface on which I depend changes then I’m potentially screwed. I take the point that systems built on platform- and infrastructure-as-a-service offerings have this coupling problem in the extreme.

The solution is to keep systems as loosely coupled as possible and to provide backward compatibility of interfaces. I think as an ecosystem forms on top of a given platform it will be essential for platform provider to support some kind of backward compatibility. Your Vista example can be extended. Microsoft has always taken great pains to maintain backward compatibility (albeit at the expense of simplicity, performance and other important factors).

There are lots of ongoing battles to see where we will collectively define platform layers in our software stacks. History has shown that platform providers who foster the largest community of ISVs tend to win out. Stranding masses of developers on a no-longer-supported set of interfaces is not a good way to go about building that community. So over time I think you’ll see fewer ‘forced upgrades’.

It’ll be interesting to see how it all evolves…

(BTW the MHT link seems to be broken)