if Microsoft put their bid in, who else do you think yahoo would look at other than google?
in a way, I'm sure yahoo would want google to bid as well to push their stock higher, but at the end, M$ wants/needs yahoo more than google and google knows this. that's why they want to push the buying price higher. I would too, the more microsoft has to spend on yahoo, the weaker they become financially. at least until the investment pays and no one will know when.