Vulnerabilities in media decoders are a prime vector for infection since they are usually processed automatically. The only reason you are seeing it in software from 'a decade ago' is that hackers face so much competition from white hat researchers when it comes to browsers, fighting for vulnerabilities from a usually shrinking pool. With fewer opportunities some are turning to media decoders found in applications like Office. It's a less effective vector since it requires several actions from the user, but the upside is that these applications are often not as aggressively patched as browsers have become which means a single vulnerability might work for months.
For a comparison it's been almost a year since the last arbitrary code vulnerability was reported in FireFox's GIF decoder, and 2 years since the JPEG decoder was last turned into an attack vector (to the best of my knowledge). IE, Chrome and Safari have experienced similar droughts, with all the major browsers only having 1 or 2 image based vulnerabilities reported annually for the last few years, and usually by researchers who allow it to be patched quickly rather then as a zero day being exploited. Of course other types of media exist. CSS/HTML5 has rapidly become a media format in of itself and a little over a month ago FireFox was vulnerable to arbitrary code execution due to the way it decoded animations in CSS stylesheets (this was reported by Google and patched with the release of FF 24). TL;DR Researchers are hogging all the good browser vulnerabilities, so hackers are playing in the dusty old rooms nobody has visited in years.