Fructose is fructose, there's no "natural fructose" however it's one thing to eat it pure, another one in a fruit
"The problem with fructose is that the liver has only a limited ability to properly process it."
Correct, glucose can replenish muscle glycogen, fructose can't (the liver produces both types of glycogen) - http://www.ncbi.nlm.nih.gov/pubmed/3592616
"This is because the fiber provides certain nutrients"
Fibers, per definition are not digestible but are other things that may happen http://en.wikipedia.org/wiki/Dietary_Fiber
And of course glycemic index may be a problem with sugars as well.