I think this can turn around quickly when actually (more) profitable slimline PSP and / or slimline PS3 products hit the market.
Nintendo is a tiny company in comparison to Sony, Sony employs over 50 (!) times the amount of people as Nintendo does (which IMO is a good thing!), Also Sony can easily afford to make huge investments they did for the PS3 as they have done over the past years and still generate healthy profits due to its overall consumer electronics performance.
Later when they generate profits from their gaming devision this adds to the overall profits. Shareholders often look at shares as a short term investment.