Preceded by a number and indicating, roughly, “… years later.” More so than “later,” “on” provides a retrospective feel, and thus is useful in titles, as in Alan Bennett’s first produced play, the 1968 “Forty Years On.” The two-letter word makes the expression especially tempting for headline writers, and as the tenth anniversary of 9/11/01 approaches, it is ubiquitous. A Google News search for the phrase in headlines yields 424 hits for just the two days Sept. 3 and 4, 2011, from “Bin Laden Wanted a Second Hit, Ten Years On” (Sydney Herald) to “10 Years On: Finally, Smarter Airport Security Screening?” (Wall Street Journal).
A Consummate Teacher: Coach Robinson 50 Years On. (New York Times headline, August 4, 1991)/Though we’ve felt the impact of 9/11, more will yet unfold. Ten years on, it still might be “too soon to tell.” (Sacramento Bee, September 4, 2011)
notoneoffbritishisms.com 
I haven’t heard this one in everyday use yet, but it’s been increasingly showing up in article titles and ledes. Probably introduced by American publisher and media types in New York who spend much of their time swimming in bi-national waters. I seem to remember it cropping up around the time of the Iraq War, when our military alliance with the Brits was very strong, around the same time that George W. Bush started using the Britishism “stand down” to mean “leave”.