There are still some things you can't do in HTML, eg. Google Pacman used Flash for sound because the HTML5 <audio> tag couldn't provide reliable timings. Google Wonder Wheel is in Flash (despite having had various HTML5 prototypes floating around) because FF/Linux's <canvas> performance is atrocious, and IE6-8 excanvas.js performance is borderline at best.
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There are still some things you can't do in HTML, eg. Google Pacman used Flash for sound because the HTML5 <audio> tag couldn't provide reliable timings. Google Wonder Wheel is in Flash (despite having had various HTML5 prototypes floating around) because FF/Linux's <canvas> performance is atrocious, and IE6-8 excanvas.js performance is borderline at best.