spam in gmail

I have been using gmail and yahoo mail for over 2 years now and am still wondering why does gmail gets the most spam than any other email server like yahoo or hotmail. It has been only a week and have to again delete about 1000 of my spam emails in gmail and my yahoo mail has about 10 spam emails, when compared to gmail user base being lesser than yahoo( i would say this because most of the spammers would try to spam as many users as they can ). I wonder if google generate all this spam, filters it to show that their email is much better than other email servers, or if gmail is far susceptible to attacks than others..