Well, your comments are on the screenshots, not on the applications. Try to use these applications for a while "to get the job done", you will get what I meant.
I have been a KDE user for years, I even contributed some patches back then. I still prefer Qt to GTK. But I whenever I can I use GNOME applications instead of KDE (with the exception of K3B).
I think the main problem can be traced back to when you say
> [In Skanlite/Simple Scan] Scan source, scan mode and scan resolution are important properties when scanning and it's very useful to have direct access to them.
Simple Scan (the GTK app) presents you two presets (Text and Image) and just guesses the rest of the details for you. And you know what? It gets them right 99% of the times. When it doesn't you can access the usual Preferences pane and modify whatever you want.
As somebody else commented in this thread, the KDE world refuses to have "reasonable" defaults in place, starting from the default theme to the good engineering practice of trying to guess as much as possible before asking questions.
PS: Transmissions was born in 2005 as a neat Cocoa application, GTK for Linux has been added soon after in version 0.6 (2006) and the Qt interface was started only in version 1.6 (2009). This is why it looks so like nice.