Originally Posted by
dragosc
My question is why these tickets are far less expensive, even though they have 3 flights instead of 2 and both go to Detroit.
Supply and demand. There is more traffic between Chicago and Bucharest, with more airlines competing, so prices are lower. Less traffic between Detroit and Bucharest, so prices are higher. The fact that the Bucharest-Chicago trip you're considering involves a plane change in Detroit is immaterial. Airline sell tickets from point A to point B, without regard for the route taken to get there.
Originally Posted by dragosc
Furthermore, would I be able to buy the cheap tickets mentioned before and just skip the third flight (the first flight on the way back)?
Absolutely not. Google "hidden city ticketing" to see what happens. The airlines regard this practice as theft.