Typography is as important on a web page as it is in any other medium. Choosing the right font for the message you want to communicate needs considerable visual understanding. It is important to know the structure of letterforms, how to deal with spacing (letter spacing, word spacing and leading) and type sizes: even if it appears on a computer screen and not on a piece of paper, your content should still be pleasing to look at and easy to read.

This image is taken from Jim Krause 's web site:

 
Moreover, designing for a computer screen has its own set of problems. The elastic nature of a web page, which has to work across different platforms and screen sizes, makes the problem worse.

It is the web designer's job to understand these issues and to address them - to maintain some kind of control when everything else is shifting. According to Web page design for designers , Ninety percent of web pages that you look at have been "poured", not designed and any current browser will take a block of text and display it on the computer screen in a reasonable typeface and size but with considerably less control than an ancient typewriter...

Some interesting suggestions about typography and web design could be found in those books:
Design Basics Index (krause, David & Charles 2004) and Graphic Design School (Dabner, Thames & Hudson 2004)

To learn more about web design and typography contact brightlemon web design london.