well, anecdotally, i think mine are, but there are SO many variables that could apply to why...good diet, healthy lifestyle, plenty of sunshine, rest, vitamins, lots of love and laughter.
some of it must be genetic. and constitution.i know kids who seem totally immune to everything, and have perfect teeth, despite eating pure junk all the time and being vaxed up to the hilt.
i also think that some kids are more equipped to handle vaccines than others. i have always had a very strong gut feeling that had i vaccinated my kids, they would have been profoundly, negatively affected by them.
also, i think family structure and lifestyle plays a big part of health and catching bugs-my dd didnt even have her first cold until she was 2 yrs old or so, and my ds, my 2nd child, caught his at 2 WEEKS. and again at 2 months. he also had rotavirus with dd last year, 2 other random stomach flu things this past year, and the flu recently. All that aside, he (and rebounds very fast, and is usually, blessedly, a bright eyed, pink-cheeked, energetic picture of health. dd also.
dd didn't have an older sibling to share cooties with her

and ds was out and about in germy kid places wayyyyy more and wayyyyy earlier than dd.
i'd be very hesitant to make a blanket statement that all unvaxed kids are healthier than vaxed kids....
edited to add...
just read the thread, and this is sort of OT...as far as nutrition triggering genetic response-made me think of an article that was posted in the breastfeeding forum not too long ago-
breast milk and genetic destiny