[wayner]

A lot of what we do grammatically and in sentence structure was to overcome the limitations of the technology of the time. Even our keyboard layout was so that we couldn't type so fast as to jam the keys in our typewriters.

Now, a lot of the technically unnecessary rules have changed as new technology makes the old readability techniques obsolete.
(Serif fonts vs san-serif, technical features and such.)

Underling is a great example of something that is rarely used as often. It has been replaced with the new advanced bold feature in many style guides.

There is no one hard and fast rule for everything. In fact there never was, but now there are even more options.

The key is that for corporate documents etcetera, that each contributor agrees on the same style. A style guide is created and shared among the contributors for consistency.