Disappearing PSN Games? Why?

I noticed recently that PixelJunk Racers has vanished from the Playstation Store, and been replaced with 2nd Lap. Is 2nd Lap an entirely different game, or is it basically just a huge patch to PJ Racers? 
 
And while I'm asking, is the same scoop what happened with Gran Turismo HD Concept and GT5 Prologue?

It's a huge patch...  If you have PJ Racers you can download 2nd lap for free...   
 
Doesn't do me any good since I got PJ Racers for free... but it doesn't show up that I bought it... 
 
But I dunno about the GT5 stuff.

Well queens blade also disappeared from the video market place awhile ago.

i hate that by the time I got a PS3 the free demo GTHDC was replaced by the overpriced demo GT5P.   
Those Ferrari challenges in the top tier are pretty ridiculous! 
& Queens Blade was like a limited time free thing anyway right?

And they wonder why we buy games used.