PSP never really sold "well" in the US, its best 12 month period was just over 4m from mid 2007-mid 2008 and its generally sold under 100,000 per month in the US since the middle of 2010, which is two years already, with the exception of a Spring 2011 price cut lift that lasted one month and a couple lousy November / Decembers.
Given how low demand has been for PSP for years (they've sold like 5.5m PSPs in the US in all of 2009, 2010, 2011, and 2012 to date), its not that surprising how Vita has launched in the West. The US is a huge market, selling 5m units in a year is pretty common now, so the Vita is facing pretty strong head winds based on how PSP has performed recently.
Sony has sold almost 20m PSPs in the US over seven years with the machine launched at the peak of Sony's power - I don't think the handheld market (for dedicated game machines) is necessarily growing any more - so Vita could conceivably perform worse than PSP, although its way early to know for sure either way.
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu
