This wouldn't be as big a story had HBO's Real Sports not depicted him as an investing savant.
Deadspin pretty much sums up the truth in this case - that Dykstra's your garden-variety financial industry scumbag who made major gambles with other people's money and lost it. Of course, I'd be shocked if Real Sports (or Bernard Goldberg) in the follow-up piece took any responsibility for building up people like Dykstra when the going was good.
It's a good reminder though - any gambler, no matter how moronic, can get on a hot streak.