You are very astute, Turnadot.
IMO, the DNA was simply contamination, probably from some source at the autopsy, where the clothes were pulled off the child and Dr. Meyer even carefully checked the crotch of the panties against the body to align the blood drops, or at the forensic lab, where the underwear and longjohns would have been handled, as well, to examine for and to collect samples, in exactly the places from which the "touch" DNA was eventually extracted. The fingernail DNA was far too degraded to be included in any "match," despite what Team Ramsey constantly misstates about it: one to three markers does not a match of ANY KIND make. But the fingernails were also cut at the medical examiners office, possibly with contaminated instruments, as Thomas stated, to that could be the source of all the contamination. DNA is inconceivably minute, after all.
About how the Ramseys got away with this: If you're willing to have your eyes bleed a little more, at FFJ I recently wrote two rather long posts--not the Bonita Papers, but I'm notorious for my long posts because I kind of think while writing--which come to rather the same conclusion.
The thread is actually titled "Bonita Papers." You might want to read the comments from the start, but specifically my two posts related to your statement are down this page a bit--#191, and then on the next page down a bit--#199:
http://www.forumsforjustice.org/forums/showthread.php?t=10001&page=16
I don't think it would be appreciated if I copied them here, though. My THEORY--I don't believe we'll ever know the truth about it--is that Lockheed Martin is the key to this mystery. In the first post I address the "bussiness" mentioned in the ransom note; in the second post, the strange responses of LE that morning.
Might help, might not: but theories are all we have.