For KDE it depends on the type of component.
All things that are part of the platform are LGPL, BSD or MIT licensed, only
end user applications are often GPL licensed.
Basic rule of thumb: anything a developer might use -> LGPL, anything only a
user would use -> GPL
Thanks, Levin for giving me clear explanation. But as far as I am aware as KDE user, some important parts of KDE still under GPL, such as KWin and Dolphin File Manager. Those are might be end user applications but sometimes developer needs to improve them with their specific needs without affected with GPL.
You probably already know if the current trend of free software seems to move away from a very radical copyleft license for more relaxed license. WebKit and GoogleChrome which are basically derived from KHTML and Android OS with the Linux kernel as its core is a small example to prove that non-copyleft license helps the wider acceptance of free software. Non-GPL software will attract more developers to collaborate together, ranging from individual contributors to large-scale corporations for the benefit of each. Sometimes an individual's involvement is not enough to manage large-scale free software projects, so the involvement of large companies are sometimes required. This is where the LGPL serves as a compromise between the interests of free software activists with a corporate interests.
Free software movement is still relevant today, but stay away from proprietary is something that is impossible in this era.
Linux Torvlads said
"I use the best tool for the job, even if that includes proprietary software."
Clement Lefebvre (Linux Mint Founder) also said:
"Freedom should be granted to the developer to decide whether he wants to distribute his source code or not. I don't see why he wouldn't (unless he's not familiar with open source and maybe scared of not generating profit... I don't know) but the thing is, this is his choice. Similarly it's your choice and your freedom to use his software or not. Having some political movement telling you to restrict your own choice and boycotting good and helpful software just because you didn't get the source code with it is simply going against your own freedom."
After all, I didn't want to start license debate. I just want to share my opinion that might useful for LXDE-Qt contributors to consider.