does advantage II for cats lose its effectivness

Hi all......

When a cat has been on advantage II for all it's life, does the cat's body become immune to it?  We had a bad bout with fleas in the yard this year and I'm guessing the fleas traveled indoor on our clothes.  The cats all have fleas and have all been on advantage II all their lives.  There are no noticeable fleas in the house....in other words, we don't find the fleas on us and don't get bitten by fleas.....I only find them if I flea comb them and they all have tapeworms.  I won't treat the tapeworms until I can get rid of the fleas. I'm just wondering why the advantage is not killing the fleas that are on them.  As it was explained to me by a veterinarian, the flea only needs to crawl on the cat who it treated with advantage and it paralyzes their mouth and they can't bite and eventually die. 

Yes, a cat's body can get too use to one particular flea treatment. I've also read/heard that fleas themselves have evolved so they can 'resist' flea treatments. (Not dis-similar to humans and antibiotics.)
Can/have you tried Revolution?

No, I have never tried Revolution.  I've always used advantage II.  Years ago, my veterinarian started me on the 50# dog dose and I dispensed what I needed per cat.  To be honest, it was and still is a cost issue with me considering I was dosing 5 cats, sometimes more every month.  I had a second opinion vet recently suggest I switch to advantage multi because it covers other issues as well.