Don't want to diminish KDE, but how is that incredible considering that for each of these there is a much more popular GTK or even Gnome project software?
KHTML/WebKit: I don't think the GTK/Gnome folks ever wrote a browser engine.
KDevelop: Did the GTK/Gnome folks ever write a significant IDE with a code model?
Krita: It's focused on painting/illustration and doesn't directly complete with Gimp. Among artists doing this Krita is likely more popular than Gimp now, since the latter isn't even in the running. (Support for MyPaint brushes is progress on that front, though painters want many other features.)
For KMail/Kontact there's Evolution, but arguably neither ever became really popular if you compare them to, say, Thunderbird.
KHTML/WebKit: I don't think the GTK/Gnome folks ever wrote a browser engine. KDevelop: Did the GTK/Gnome folks ever write a significant IDE with a code model? Krita: It's focused on painting/illustration and doesn't directly complete with Gimp. Among artists doing this Krita is likely more popular than Gimp now, since the latter isn't even in the running. (Support for MyPaint brushes is progress on that front, though painters want many other features.)
For KMail/Kontact there's Evolution, but arguably neither ever became really popular if you compare them to, say, Thunderbird.