Not so. I was bitten by a tick while working in the woods in the mid 90's. I was healthy as an ox before I was bitten. My immune system was strong. The tick still targeted me. I was fresh meat.
I got a bullseye rash and got very sick. Feverish, aching real bad in the joints and chills IIRC. Was dating a girl down in the city (Dearborn, by Detroit) and went to see a city Doc down there. He listened to my symptoms and looked at the bullseye rash and said "Very interesting. I have not seen this before." He gave me 4 days worth of Tetracycline and sent me on my way. I immediately started feeling better after taking the anti-biotic. Who knows, I may still have Lyme disease. I have read that if it is not completely eradicated by a lengthy anti-biotic regime, that it can become chronic and cause all sorts of weird shit.
Why do you think ticks would only target those with weak immune systems? It does not matter to the tick, as he is merely after a blood meal.
Fast forward to 2009: I'm sitting in the living room watching a flick and all of a sudden my left toe goes completely numb. I pull my foot up and there is a tick feeding at the base of the toe by my next toe. I pulled the son-of-a-bitch off and after a while the feeling came back into the toe.