"Oranges have pulp."
You are right, we wouldn't say Obstfleisch. There is not that much of a difference because both words refer to fruit. However, "die Frucht" refers to only one fruit. The plural "die Früchte" refers to several fruits which can be either all of one kind (all of them are apples) or mixed (apples and bananas and strawberries). "das Obst" is a singular word, yet it always refers to a number of fruits. For me, personally, Obst always refers to several kinds of fruit. Also the word for "fruit salad" is "Obstsalat".
I hope this helped and doesn't make things even more confusing..
well, unlike French. In French it is mandatory to put articles before noun. While in German, we can both use the with or without the article. The article is just the same meaning as "the" in English
Orangen = oranges
die Orangen = The oranges
Hope that helps ! and correct me if I'm wrong ! :)