Google takes some entries as backlinks some not

On the same page of web.de some links are used as backlinks some aren't

[zgb999]

When I search for backlinks I find that the page
a category of the German web.de Directory shows up for one site.

On the same page of web.de are many other links going out and I checked some.

The strange thing is that some others I checked don't show a link from web.de on Google.

The same kind of behaviour I found on other directories too.

Why is Google treating sites on the same page differently?

[edited by: heini at 6:12 pm (utc) on Dec. 11, 2002]
[edit reason] took out specific urls [/edit]

[heini]

That is a good question. What puzzles me most is the links are displayed at all, even if it would be only in one instance.
The links from web.de are jump urls.
Now Google has no problems with those, and it's clear web.de links count as backlinks in Google. But I was of the opinion only links from categories which are very high in the tree would muster enough PR to be shown by Google as backlinks.

[dvduval]

I've noticed this also. Could it be that Google has some sort of relevancy filter?
Could there be a relationship with Google Sets?
[labs.google.com...]
or Google Quotes?
[labs.google.com...]