The word "asterisk" does indeed have different meanings that is why ddg uses this particular technique to disambiguate the query. Narrowing down the meaning is performed by the user's intelligence not machine intelligence. There on the first page one can see high level "asterisk" meanings including Asterisk PBX, one click away. Please note too that Asterisk the PBX is indeed top of the weblinks section.

Compare the usability to google search. Notice that a person searching for the song "Asterisk" by M83 can find it immediately on ddg. A google user would have to try different keyword combinations to eventually get the topic in question - say "what was the band's name again?" and you are off on a wild goose chase. In all honesty I would rather click that disambiguate menu than have to retype a whole bunch of search terms.

Secondly your "yate" query is in fact the first weblink result of ddg (http://yate.null.ro/pmwiki/), the other top bits help the user disambiguate the search as there are other meanings to the name Yate. A possible reason Yate the softswitch does not show up on the disambiguate menu, could be the same reason why Yate softswitch does not show up on a disambiguate menu in Wikipedia. If you create a well written wikipedia entry, I believe your softswitch would appear shortly in ddg disambiguate menu. It seems the only like to the Yate softswitch from wikipedia is this link http://en.wikipedia.org/wiki/Jingle_(protocol)

As an experiment, try find those little Yate towns with the keyword "Yate" and the song Asterisk by the band M83 with the keyword "asterisk" in google.

How about one more thing: search for Asterisk in ddg, click on the disambiguate link for asterisk and notice that the results filter out non Asterisk PBX results. Quite handy if you are an Asterisk PBX professional.