What do these things have in common? During the weekend I was at at a conference of economics (weird, isn't it?) and one of the presenters talked about how we must look at the economics if we want to achieve a given goal, for example protecting the environment. For example currently the computer manufacturing companies have no incentive to create a long living product because they sell them and their goal is to sell more. However usually we don't buy computers because we need computers, but because we need some services. What he suggested was that if we would buy the service instead of the object (so that the computer would be leased to us instead of sold), the manufacturers would have an inherent interest in ensuring the longevity (both in the sense of quality and in the sense of being able to fulfill the given service) of their products, which in turn would reduce the environmental damage.
All this fits in nicely I think with the rush of AJAX-y / Web 2.0-y web applications that we are seeing. Because this liberates us from depending on a given computer / operating system and usually you don't need a heavy weight machine to use them. This is a step in a "software as service" direction, so it might well be that if you are using Google Reader, you are helping the environment :).
On a more technical note: there are many advantages and disadvantages to these kind of "applications", many of which have been already discussed years ago during the thin client versus fat client debate. It might well be that this is only a temporary phenomenon made possible by the increase of available bandwidth and that in the future the balance may again shift if the available bandwidth / average application size changes in the opposite direction (which I think is the main reason for choosing one solution over the other)