Maybe Sony just doesn't see a lot of value in releasing a PSP2 right now. They always introduce "new" storage mediums with each of their consoles (CD, DVD, Blu-Ray and UMD) and the PSP Go was them trying to introduce online distribution for their handheld (which they planned to implement in the next PSP as well, most likely). Maybe they'll introduce a PSP Phone one day (but that would be a "phone first and games second"-device because no one wants to pay a monthly contract to use a handheld console :-p ) or a PSP with an integrated high-res camera, who knows?
Currently they might find it valuable to just focus on the Playstation 3. They are finally in the black again with their gaming devision, they should only risk huge R&D costs (and manufactoring costs) for a PSP2 if it is 100% worth it. They lost over 3.5 billion dollars over the past 3 or 4 years during the PSP/PS3 era and they have to stay competitive in the home console business (price cuts, etc.). Maybe they could risk another year in the red numbers (because of a PSP2 launch), maybe they can't, I don't know I'm not a Sony insider.
But I'm rather sure if Nintendo released a Wii 2 before Sony was able to recover from the huge PS3 losses while losing money because of a new PSP at the same time they'd be in a bit of trouble.
It's a bit like the current situation of most western states - they were able to fight the financial crisis by increasing their debt but in case there's another crisis they are in deep trouble.
