Styling two tags in similar ways: Preferences

[CJM]

I'm working through Eric Meyer on CSS (a good book).

In one example, he uses the following styles:

a:link, a:visited {
background-color: Transparent;
font-weight:bold;
}

a:link {
color:#171;
}

a:visited: {
color:#747;
}

I was just wondering if there were any reasons (other than preference) that
he chose this route rather than just defining both tags seperately?

E.g.

a:link {
background-color: Transparent;
font-weight:bold;
color:#171;

}
a:visited {
background-color: Transparent;
font-weight:bold;
color:#171;
}

Cheers

CJM