I hear this all the time, but as a bird biologist who has worked with a number of the researchers who did the eaarly egg shell work I can tell you that the science from the "in lab work, controlled experiments" is tight and has passed all sorts of scientific peer scrutiny. There are many in the industry who would like to explain it away through wishful thinking. The manufacturers continue to make DDT and sell it to many third world countries. DDE the metabolite of DDT continues to weaken egg shells in birds in the rest of the world. Many of the imported fruits, including bananas and others, have measurable residues of pesticides banned here in the good ole US of A.
Farmers in Central and South America still spray chemicals that have been documented to kill wildlife directly. Not any of this maybe yes, maybe no, possible egg shell thinning. The birds fall dead out of the air.
Catbird can probably expound on this and likely has specific technical knowledge, but it isn't pseudo-science.
All I can say is that I have read and heard contrary claims about the effects of DDT, its usage (and banning) worldwide, and so on. Again, it would be nice to have a global fact-checker somewhere.
Any google search will show you what I mean (e.g. http://www.junkscience.com/ddtfaq.htm).