It just goes to show that the reason that IE got to have so much dominance was not because it was bundled with the operating system, but that for far too long it had no real competition.
I rather think that it means you're looking at the data too late. Of course MSIE was the dominant browser when it didn't have any real competition, but that was after the competition had been killed off. Before that, there was healthy competition between Microsoft Internet Explorer and Netscape Navigator.
Although it is impossible to say for certain, many believe that MSIE came to have ~90% market share through a combination of being bundled with the operating system and having become good enough that it wasn't worth the trouble to get a different browser. Netscape went under and it would take years for Mozilla to produce something that people would actually prefer over MSIE, but all this time, there had been Opera, who have made a very impressive browser at least since their 3.x days. Why is it that they never managed to sway a large percentage of users? Could it be because Opera, other than Netscape and IE, was never included on ISPs installation disks, included with shareware magazine's distributions, or bundled with operating systems on large scale?
Recent history also tells some interesting stories. At some point, Microsoft apparently got worried enough about the competition on the browser front that they created an Internet Explorer team again. Yes, they had actually disbanded the IE team after the release of IE 6. So what did the competition have to do to get back in the game? Well, take a look at Firefox, Opera and Safari from around Firefox's 1.0 release, and you will find that they are light years ahead of MSIE 6 - which really isn't all that different from MSIE 5.5. Let's also not forget that Firefox had a stable base on *nix, and Safari on Mac OS X, so they would continue to be improved regardless of adoption by Windows users.
Does bundling a browser with the operating system (or ISP service) give that browser a huge advantage over the competition? I think it is clear that it does.