Even though these technologies make you believe that content is being pushed to you, the truth is, under the hood these are just smart clients that actually make connections to servers to receive frequently changing information. However, push technologies haven't really taken off like the more traditional Web pull model has, and so we have been seeing some of the companies closing shop. Because no standard protocol has been defined for the exchange of push information between push servers and applications receiving such content, it is impossible for clients or servers of different vendors to talk to one another. Providers of push content can never depend on software from one vendor because they were unsure whether it would ever reach a large user base. Similarly, users did not want to use three or four different push clients to receive content from different providers and at the same time wouldn't have liked to be stuck with a particular content provider just because they were using a client from one particular vendor.
Standardisation is what makes competition thrive and technologies succeed in the marketplace.
This fact is very evident from the runaway success of GSM mobile phone systems all across the world, when there were other systems that were slightly better in terms of efficient use of radio spectrum. Standardisation is what made GSM commercially successful, and now it is this same reason that is making this system evolve into a third-generation wireless network of tomorrow. Once commercial success was achieved, it was easy for this system to improve in areas where it was not as good as other mobile phone systems. You can't push information to a user unless that user is actually using their workstation and if the person is in front of it, you might as well push information using standard e-mail. Since they already monitor their inboxes regularly, it doesn't make sense to try to grab their attention using some other mechanism.