Firstly, when you assign your software to GNU GPL v2, you are still the copyright owner. It is STILL your work, and you still have say over your software. You can REMOVE the GNU GPL at any time, and do with it as you wish, but you CANNOT revoke the copies that were made by (given to) other people. They can still modify that portion of your program as GNU GPL v2, and you STILL are the owner of its copyright. You will always be the copyright holder of the software, for as long as the laws of copyright in your country permit. If you release your software into the Public Domain then you NO LONGER are the owner of the copyright. In fact, no one owns it – it belongs to the public so to speak.
Speaking of releasing software, a speaker at a free software conference got a few chuckles with his slides on programming language history. You have to imagine the following are projected sequentially (don’t complain to me about the years, I was never good at exact history):
Slide: 1956 Fortran language released
Slide: 1972 C language released
Slide: 1983 C++ language overpowers its jailers and escapes
Needless to say, he wasn’t promoting C++ in his talk.