As you know, Microsoft had more than 90% of the OS market worldwide. While other OSes did exist, they didn’t provide meaningful competition. The person to which you replied meant that Google Milk is only a problem if Google abuses its search monopoly to push the market away from other milk vendors, not that Google isn’t a monopoly as long as another search engine exists. Their main point was that it isn’t abusing a monopoly to launch a broad array of products if each of those products compete in a fair market.