yahoo and msn are more easily gamed than google. so, in general you will find a lot more sites with blog backlinks and sitewide link buys listed in yahoo and msn than you will google. this is only generally speaking of course. google allows its fair share of spam in their serps too (just look at some of the pages now). the difference is that google will get rid of most of those spam pages in time while yahoo and msn will likely keep them ranking.