According to me only very old webmasters or may be some big companies like hosting ect and other online companies would preffer to try and submit their sites to Yahoo cos for them that amount would be negligible before the thousands of dollars spent on
SEO and marketing.
No one else would be intrested.
May be Yahoo wants the same thing to happen. By doing that they are infact keeping a huge amount of spam away without any special efforts and moderation required. May be thats the reason.