How come GPL code becomes un-GPL and then disappears

[GMAIL - James McDonald]

A long while ago a company named Postpath developed an Exchange drop-in 
replacement using a host of OSS. Postpath was then purchased by Cisco 
for a squintillion dollars.

If the purpose of the GPL is to keep code open and free. How is it that 
the code doesn't appear to be available in the public domain?

I noted the same thing about an application that was made as an 
interface to my ISP's SMS gateway. It was released via GPL which was 
then made closed source and any links to the original code disappeared. 
So a timeout period seems to apply get it while it's hot because even if 
it's GPL'd now we will close it off later.

I appreciate that you could write a non-GPL module that then called GPL 
code and keep that code closed. But when the non-GPL code embeds so 
deeply into and changes the GPL code where is the line for maintaining 
GPL compliance (passing the mods on).

Am I missing the point of the GPL?