Well, the Cheesecake Factory is a bit of an outlying case -- those portions are ridiculous even by American standards. But as an Australian living in the US I agree with you -- I find it hard just to get a normally-sized meal for breakfast or lunch.
In Australia, if you order a ham and cheese sandwich, you get ham and cheese. In America if you order a ham and cheese sandwich you get a huge stack of ham, a bit of cheese, lettuce, tomato, pickles (!?), maybe some sprouts, mayo and a bright yellow mustard-like substance. If I tell them I just want ham and cheese they look at me like I'm crazy (and I am, cuz I'll be paying about six bucks for this sandwich anyway).
On the other hand, last I heard Australian rates of obesity have overtaken US rates. On the other other hand, Australia probably has more of the slightly-fat people (ordinary folks with big beer guts) and fewer of the ridiculously-fat people (acres of waddling flesh or too-fat-to-walk electric wheelchair folks).