Sony has revealed that the original launch date for the Vita in Japan was the 3rd of December or (12/3 in US date format).. but held off a couple of weeks to build up supplies of stock. That makes it pretty clear that there was never any hope of a western launch in 2011 as the last thing Sony would want is a paltry number of consoles spread around a number of territories.
Instead, Sony looks to able to keep the rapid horde of Japanese gamers supplied, plus all the high-hopers who want an export unit. No doubt that'll attract some of the gangster types who plagued the iPhone and iPad launches (getting tramps to buy units, if memory recalls) so they could sell them at inflated prices.
It still looks like March is the best bet for a western release, although the way our economies are flailing around, who'll be able to afford one?