All search engines use Robots (bots) that constantly search all the websites for information and then catalog them.
Yahoo and Google might get slightly different results, as do other search engines is due to the different algorithms they use to power their bots or due to the way they think the information should be looked at and displayed.
It is similar to if I asked 20 people to search a library and find me every book relating to
"paint", I probably will get several different answers. The difference is that the library does not change much on the other hand, pages on the internet change constantly, new website, updated pages etc
Yahoo and Google might get slightly different results, as do other search engines is due to the different algorithms they use to power their bots or due to the way they think the information should be looked at and displayed.
It is similar to if I asked 20 people to search a library and find me every book relating to
"paint", I probably will get several different answers. The difference is that the library does not change much on the other hand, pages on the internet change constantly, new website, updated pages etc