The technology used is irrelevant per se, the UserInterface alone distinguishes a medium from another: Several protocols use TCP/IP, and several user interfaces use the same protocols.
Certain content is best transported with certain media. Example:
Music is best transferred via radio. If the content consists of music and video, then it is best transferred via tv. Transferring music via email makes little sense: Encoding the data consumes much more space than usual mails, therefore disrupting mail for other people. Sound and electromagnetic waves can be broadcast, mails cannot (they can be copied, thus wasting even more space). Encoding and decoding music sent by mail takes much more time than using your stereo.
Therefore, consider whether the UserInterface you are thinking of is not better off using another medium. Consider whether the user interface you are thinking of has not already been implemented using another medium.
When something looks like news, is read like news, is replied to like news, is archived like news, is treated like news, then don't put it on the web, use UseNet. The web makes things more difficult and reinvents the wheel.
Some of the argument above seems wrong. Some mediums are multipurpose and/or adaptable to other uses. For instance, with MultipurposeInternetMailExtensions (MIME), e-mail is not longer just for letters. Similarly, the web is definitely an adequate medium for news, whereas UseNet is not (not enough people read it). Simple media like e-mail and the web have a better chance for adapting than complicated media like a wiki, but a complicated media have a better chance of doing a better job. So, the end result comes down to business reasons. Is having more than one medium worth the extra effort, or is the overload of the old medium sufficiently useful to not value the complication of having yet another medium.
Note how many stories make successful books but fail as movies? Harry Potter was nice, but boring. The Lord of the Rings was nice, but very long and strange for newbies. The reverse is often trivially true as well. The Star Wars books are shallow. Star Wards comics are shallow as well, but shallowness in comics is often not a drawback. The Making Of... books are movie-related books that sell. What does it all mean?
The question to ask is: What makes this a good story? And then think about the media used to tell the story.
Books are long, full of detail, descriptions, plots, side-plots, interesting ideas, complex and fascinating: They are intricate. Movies are comparatively short, action packed, play with light and colors, have witty and fast dialogs, slapstick and funny faces. Images come to life.
Thus, what happens when you transport a story from a book to a movie? The two most common outcomes:
No matter what you do, people will be disappointed, either because you changed the story too much, or because the movie is boring. Nevertheless, a lot of people will go and see the movie, so it will be an economic success anyway.
There's another option, of course: Failures.
Or the exceptions: Successes.
Shakespearean plays, on the other hand, are already something shown to people waiting in the dark, but are almost always shortened when they become movies. Example: Romeo + Juliet. The reason is unclear, as plays cater to the same experience: Spectators are passive, "waiting in the dark", and they both have a similar time frame (a few hours). Perhaps that's the difference: Movies are not expected to last longer than two hours, thus three hours are exceptional. Plays, on the other hand, are longer. Thus, media have a tradition to consider, as well?