Aside from the fact that IE being bundled made it far less likely for someone to go looking for another browser, they were shut out from being bundled by OEMs and ISPs through restrictive covenants[0][1]. It obviously wasn't impossible to install Netscape, but situations where Netscape was the user's first entry to the web became extremely unlikely.

This isn't really controversial, it was one of the major factors of the antitrust case against MS, and MS didn't argue they didn't do it, only that it wasn't illegal afaik.

[0] http://www.businessweek.com/1998/42/b3600109.htm [1] http://www.justice.gov/atr/cases/f2600/2613toc_htm.htm