To the first question, my guess is that yes, you have lost some kind of immunity, but the reasons of this lost may not only lay on your habit of avoiding raw food, and tap water, but in the practices of all the Western culture.
I do not know how to quote properly, but here it is something I found in an article in the New York Times Magazine (May 15 2013):
A handful of microbiologists have begun sounding the alarm about our civilization's unwitting destruction of the human microbiome and its consequences. Important microbial species may have already gone extintc before we have had the chance to learn who they are or what they do. What we think of as an interior wilderness may in fact be nothing of the kind, having long ago been reshaped by unconcious human actions. Taking the ecological methaphor further, the "Westernized microbiome" most of us now carry around is in fact an artifact of civilization, no more a wilderness today than, say, the New Jersey Meadowlands
The title of the article is"Some of my best friends are germs", by Michael Pollan.
The next paragraph of the one I just quoted says:
To obtain a clearer sense of what has been lost María Gloria Dominguez-Bello, a Venezuelan born microbiologist at New York University, has been traveling to remote corners of the Amazon to collect samples of hunter-gatherers who have had little previous contact with Westerners or Western medicine "We want to see how the human microbiota looks before antibiotics, before processed food, before modern birth", she told me. "These samples are really gold".
So, my guess is that not only you, who, I assume, are a Westerner, but a lot of us who live in the Western world, or in places who have the same practices , have a less strong immune system, because of the practices our culture has.
Take this, as an example, also, from the article I cited before:
One bacterium commonly found in the non Wester microbiome, but nearly extinct in ours is a corkscrew-shaped inhabitant of the stomach by the name of Helicobacter pylori. Dominguez-Bello's husband, Martin Blaser, a physician and microbiologist at the N.Y.U., has been styding H. pylori since the mid 1980s and is convinced that it is an endangered species, the extinction of which we may someday rue. According to the "missing microbiota hipothesis," we depend on microbes like H. pylori, to regulate various metabolic and immune functions, and their disapearance is dissordering those systems. The lose is cumulative: "Each generation is passing on fewer of these microbes," Blaser told me, with the result that the Western microbiome is progressively being impoverished.
The article is very interesting and informative.
The answer to the second question, I guess is yes, for the same reasons mentioned in the last sentence I quoted.
Of course, when you, or me, travel, we are at risk. Our immune system, may not respond properly to the microbes found in the new environment. But I believe, this apply also in the opposite sense. We may carry diseases for which the native people's immune system is not properly armed to fight.