The thing is, their players rarely do as well outside of Oakland.
I mean, McGwire and Giambi both were good... You could point to Hudson as another...
but... Tejada? Zito? Both have been bad ever since. Mulder? didn't do anything... more recently, Haren? Cahill? They basically turned into great trades for Oakland...
even Rickey Henderson never was as good outside of Oakland as he was in the white shoes...
The only trade that I really hate we made was Street and CarGo for Holliday. That turned out as a downright failure... and it was a traditional style gamble that Beane really doesn't make usually. doesn't matter though. Beane fleeces everybody so fucking hard most of the time.
For example, Rich Harden? turned into nothing for the Cubs, turned into Josh Donaldson for the A's.
So, really... Oakland not keeping their players is far less of an issue than you'd think. Just makes them way way WAY more scrappy of team.