This is not correct. Bitcoin is under the MIT/X11 license which allows people to restrict or close it up as they like. Also, even if Bitcoin was GPL'd and they tried to pull this, their
Technically SolidCoin is violating the bitcoin license due to the removal of the COPYING file in the source distribution which has this text:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
Not to mention the global replacement of the copyright notice of the bitcoin developers in all the source files to be 'solidcoin developers'.