Still, Android has ~52% of the market. The antitrust laws used against Microsoft were due to the fact that Windows was nearly all of the market, both home and business. Plus, people using Apple now can switch off of it, unlike Microsoft at the time which had no viable options.

There are other markets than the US and the antitrust laws were employed against Microsoft in the EU.

The US antitrust case[1] referred specifically to browser vendor lock-in.

[1] http://en.wikipedia.org/wiki/United_States_v._Microsoft_Corp.

As did the European case, ultimately forcing them to give a choice to the user which default browser to download, if I recall correctly.