Assuming, for the moment, that the 98% figure is correct... the answer to your question is 'zero'... if the browser is capable of using HTML5. That list includes Chrome, Safari, Opera, Firefox, and... MSIE 8. (Though that last one has only limited HTML5 abilities. Allegedly MSIE 9 will do better.) Anyone who has a modern browser can access HTML5 sites without a problem. And, most important, they _DON'T HAVE TO USE A BUGGY, MEMORY AND CPU HOGGING, SCUM-SUCKING, ABORTION OF A PLUG-IN TO DO IT_.
Anyone who has WinXP can update to MSIE 8 for free... except for those poor slobs who work for luddites who require MSIE 6. Mickeysoft all but begs users to please, please, PLEASE drop MSIE 6 and at least go to 7, and if you're at MSIE 7, to consider going to 8. They've been trying for _years_ to get people to move on.
If you don't want to move on, then that's your problem. If you're working for luddites, then what are you doing cruising the Web on a company machine looking for video, anyway?
Get real, twit.