Only one study this author is aware of directly addresses the persistence of touch DNA. Raymond et al (2009) conducted an investigation into the persistence of DNA at crime scenes. They applied known quantities of “buffy coat” DNA (the white blood cell and platelet layer of whole blood) to gloss-painted wooden window frames, pieces of vinyl (to simulate handbags), and control samples consisting of glass microscope slides. Not surprisingly, they found that the chance of recovering DNA from an outdoor crime scene decreases significantly over time with two weeks being the major drop-off point for most of the samples. The control samples fared much better, with full profiles able to be developed even after six weeks (the longest time period tested).
http://ryanforensicdna.com/touchdna/Unless Madeleine was bleeding when placed into a vehicle it is unlikely she would have left more than touch DNA and the chances of finding that in a car 10+ years later are very very very remote. Now lets have less of the namecalling please.