Earlier quoted context omitted.
The existence of alternatives does not negate a monopoly argument. Netscape, Opera, and other browsers existed when Microsoft was slapped down for IE. Google captures somewhere around 60% of the email market share - a dominant position from which they need to be careful about what actions they take. As noted in response to a sibling comment, the presence of alternative providers has proven to not to be a reliable rem…
> The existence of alternatives does not negate a monopoly argument. It's suggestive evidence. But no actual “monopoly argument” has been made to negate. > Netscape, Opera, and other browsers existed when Microsoft was slapped down for IE. Sure, but IE wasn't the monopoly they got slapped down for, it was the thing they got slapped down for trying to drive with their PC operating system monopoly. So the existence and…
It was directly related, because it threatened Microsoft's OS monopoly by providing platform independent content. And so, Microsoft directly attacked Netscape and others.
"Judge Jackson finds that Microsoft was especially concerned about technologies, such as Netscape’s Navigator browser, that could support platform-independent computing and thereby erode Microsoft’s position. In response to the Netscape threat, Microsoft undertook a broad array of anticompetitive practices to increase the market share of its Internet Explorer."[0]
But you're right, it's not the alternatives that really matter - it's using the power associated with being a monopoly to negatively impact consumers. Google has an effective monopoly in many areas (including email), and as such practices which were OK when they were smaller are no longer going to be considered OK.
[0] http://www.pff.org/issues-pubs/pops/pop7.4microsoftmonopolyf...