The Windows 7/Mac OSX example is absurd, but there are plenty of genuine instances where Microsoft emulated and enhanced an existing product, and ended up as the market leader-- Word followed WordPerfect and WordStar, Excel followed Lotus 1-2-3, and IE followed Netscape.

The more interesting (and difficult) question is to what degree their overcoming the lack of first-mover-advantage was due to a superior product, and what degree was due to leveraging their strength in the OS arena.