I forgot that the 2006-2007 (and later?) WRX/STI had aluminum suspension members. But I would count those as sports cars. Maybe my definition of sports car is more liberal than most people's?
But, I would go as far as to say that a BMW is a sports sedan. While there isn't much special about an entry level 3 series, it is still marketed to a different crowd than your average midsize sedan buyer.
Lighter suspension = less unsprung weight = lighter spring (or better body control with same spring vs steel)
Infiniti and Lexus are also marketed towards a different crowd than your average Camry/Accord/Mazda6/etc buyer.
Like I said before - it's gonna happen regardless. Even my 22 year old Toyota (which has only been driven in snow twice in it's life and routinely kept in a garage) has some corrosion. I'm from New England where they salt the roads and things get rusty with a quickness. For me, cars have a 10 year shelf life, partly due to rust. But, I might just have a different view of what's normal for rusty cars!
Where I would draw the line is when corrosion has prematurely (less than 10 years, like in the 5-7 year range) caused significant structural degradation warranting replacement of items that wouldn't normally be replaced (i.e. control arms). Hell, if anything - I'm more worried about the electronic parking brake failing than corrosion!