It doesn't surprise me one but that those studies were done by, or funded by, a diaper company. As much as I DO believe, that you should wait until they're ready, I truly believe that all children are ready before 2 years old though. Based on my experience at least. It's almost always the parents who aren't ready to start potty training so they miss the window of opportunity.
Anyway, My brother and I were both potty trained at 18 months. All of my cousins' children were trained before 2 years of age. I have friends who admit they skipped potty training when their kids were 2 because they (the parents) weren't ready to commit to it, and their kids ended up being in diapers til over 4 years old.
My oldest daughter understood the concept at 18 months, but she wasn't ready. So we talked about it quite often, got a book called "Big Girls Use The Potty" and rught before her 2nd birthday she decided she was going to use the potty and completely, fully started doing so from there on out. Within 2 days she was into underwear 24/7.
My youngest daughter saw her older sister using the potty and wanted to try at 20 months. She took longer to train (3 months), but now at 23 months, she is completely potty trained and in underwear 24/7. She went through very distinct phases of poty training. We started with letting her run around the house with no bottoms whatsoever - just a long tee shirt or nightgown - for about 2 months. Then we put undies on under those long shirts while at home and she had quite a few accidents for 2 days until she figured out that they undies were not diapers! At that point she could wear undies, but only dresses out of the house because if she had on shorts or pants, I think that made her feel like she had a diaper on she would pee. So we did a couple of days strictly at home wearing undies and shorts so she could start to realize that shorts are not like diapers! This all went on for about a month and now she is 23 1/2 months and wearing undies with shorts all day whether we're home or at the store or at the park. She hasn't had an accident in 2 weeks!
I believe, that it all comes down to good teaching skills, patience, and committment on the parents part, without forcing. (Just in my opnion! - Don't want anyone who's kids are over 2 and still in diapers bashing me with comments that I'm judging them! ;)
Good luck!