I think you are right in some ways Sandie.
There are of course geographical differences where some places are more likely to be the habitats of some organisms. This is true for lyme disease for example, where the bacteria that cause the disease is transmitted by ticks. If a cat is strictly indoors, there is no way that he will get any ticks & spread it to people. People would get the tick by themselves. And a tick is not something to be missed out (usually). You can be treated way before spreading it to your cat I guess.
As for the fleas, if a house isn't previously infested by fleas (fleas, flea eggs), again a strictly indoor cat will not get fleas by himself. If people bring fleas from the outer environment, the fleas can live not only on the cats but on humans, too...Good old vacuum cleaner can clean the already present flea eggs at home, so regular vacuuming is a better idea than using flea products regularly. Or using pesticides for the lawn if there is a suspicion of flea source. Also some families prefer not to take off their shoes as they enter home. This can bring lots of microbes/parasites not only to our pets but to ourselves also.
I have just visited Revolution's web site & it says that it's a topical parasiticide. And since it's taken into the bloodstream (which is not better actually) it has got lots of side effects. I don't know, I still don't think that it should be given to indoor only cats regularly unless an infestation occurs or unless there is a very high risk of infestation. It's like taking pain relievers everyday although you don't have any pains ! But this is my idea of course
Well develeoped countries are more prone to diseases such as cancer, asthma, allergies, & autoimmune diseases. This is also true for the animals in these countries. Exposure to dangerous chemicals in long terms (such as preservatives BHA, BHT, ethoxyquin in food, thimeserol in vaccines, or chemicals in the air), pharmaceuticals, are some of the reasons as well as hygiene is another one ! (Living in cleaner environments, people aren't exposed to a wide variety of pathogens during their childhood. So their immune system responds excessively to even harmless substances)... For example vaccinating kitties very often (combinant 4 in 1 or 3 in 1 vaccines ) may harm their immature immune systems in the longer term even they don't show any sypmtoms at the time...Vaccines also contain preservatives which again when accumulated in the body may cause harms in the long term...Sometimes they are way convenient & beneficient than harmful of course. But they are not magical things always ! (So aren't all the medicines). So one (or the animal) shouldn't get all the vaccines in the market unless he/she/it isn't highly under the risk of getting the disease. For example I have learned that the lyme disease is prevelant in non-urban areas of the northeast, mid-atlantic states, upper midwest, and northern California and Oregon coastline & the people who engage in outdoor recreation (e.g., golfing, gardening, hiking, camping, fishing, hunting) or have a high-risk occupation (i.e. one that requires an individual to spend most of his/her working day outdoors) are under higher risk of getting the disease...Everything adds up without us recognizing them & when we grow older we have to deal with these diseases unfortunately.
Love & peace