Exactly. Sony is strongly comitted to their 10-year plan for the system - they wouldn't invest in AAA titles like "The Last of Us" if they weren't, plus the PS4 isn't compatible with PS3 games. The PSTriple isn't going anywhere just yet, and although the price will drop a little due to decreased interest in the system, don't expect mirracles.
What affected the price most would be the price of a new PS2. They've been going for a hundred € or something and thus, the used prices will be a lot lower (=50). In the case of the PS3, if the console sells for 200 new, it'll take a while for it to be 50.