It might be a viable strategy, but hardly an easy step. If Microsoft simply offered it as an option, it's unlikely that anyone would care.

"Hey users, download this and block Google ads!"

Users say, "What are google ads and why should I care about blocking them?"

Or, Microsoft sneaks a blocker in via internet explorer and enables it by default. If they're lucky, it won't break anything else and Google won't be able to hack around it, but either way Google would sue.