It's a better than average explanation of the scandal, in that it contextualizes the timing with a change in the regulatory environment. Basically, VW cheated, rather than comply with a new, lower standard.
"In 2007, EPA reduced the upper limit of nitrogen oxide (NOx) emissions as part of its Tier 2 emissions program to address air pollution from passenger vehicles. Coincident with this, Volkswagen suspended sales of its diesel passenger vehicles, which could not comply with these standards that now forced diesel vehicles to be just as clean as their gasoline counterparts.
By 2009, however, the turbodiesels were reintroduced by Volkswagen—apparently under false pretenses. Volkswagen (under vehicles sold under both the VW and Audi brands) implemented software in the emissions controls package that only fully turned the emissions control systems on when the car was being smog-tested. This allowed it to pass emissions tests—but during normal driving conditions the vehicles continued to emit smog-forming pollutants at pre-Tier II levels, which were 10-40 times higher than required by law."
So while I _thought_ that buying a pre-2009 VW diesel would get you clear of the problem, it only gets you clear of the cheating by moving you back to an era of looser regulation. Tough times for diesel car owners who wanted to save a little money at the pump and maybe help the environment a smidge.