But latex and word are usually for printing a document. For something that will later be printed, you would want some sort of control over the actual look as the appearance is a large part of what is being communicated. Printing is also much more expensive than sending electrons so you would expect a much more developed medium for this.

I have never printed an email in my life. The appearance of the text is not essential to what is being communicated. Here a certain consistency is more important that variety - or rather the variety comes through the vocabulary and written expressions, not the font shape.

The same could be said for IM clients or IRC. Except for a few minor tweaks such as html links there is no real need for text formatting in these mediums, and very few clients even make the effort to do this.