how is it that some peers do not allow downloading?

[smpwrflgard]

when looking at the properties of torrents, mousing over peers, gives certain info. such as "We would download from this peer if they would let us".
How is it possible for people to not let downloading occur?
especially when they are uploading the torrent from me.
so its not a two way connection.
some of the peers are listed as having 100%, also.
I think there should be away of blocking those who are not into two way connections.

[lazybones]

It is possible that the peer has no available upload slots but has parts your client needs.. So it appears in your list but is not currently allowing more connections.

[smpwrflgard]

OK.
upload has more speed than download no matter what i do to limit upload.