I opened man page for IFCONFIG(8) in yelp. At the end of a page I've found following lines:

SEE ALSO
(8), (8), (8), (8), (8), (8), (8), (5).
http://physics.nist.gov/cuu/Units/binary.html - Prefixes for binary multiples

When I looked at the same page in console, I saw following:

SEE ALSO
       route(8), netstat(8), arp(8), rarp(8), ipchains(8), iptables(8), ifup(8), interfaces(5).
       http://physics.nist.gov/cuu/Units/binary.html - Prefixes for binary multiples

Obviously key words of links are missing in yelp.

I'm using Ubuntu 10.04 Lucid Lynx. Yelp version is 2.30.0.