I would guess that it gets you used to sweeter flavors, craving more and needing more to hit the same level of sensation once you'd acclimated.
I believe I've seen studies that show that even artificial sweeteners leave you with a sweet tooth that cause you to seek out more sugary foods without realizing it.
I know from personal experience, that after I had stopped drinking soda for a while, when I try it again I find it cloyingly sweet. I can't stand the stuff. But for people who have been used to drinking it for years, it tastes perfectly normal.
I agree. Since I've decided to stop drinking cola and such beverages (about 8 years ago) I'm surprised how unpleasant and over-sugared their taste seems to me now. But this goes both for sugar and fructose - once the habit is broken, you really don't need it anywhere.