if i'm remembering this right, it was just after the end of secret invasion; and norman didn't outright take over stark industries, he just got all of stark's government contracts. when osborn killed the skrull queen and it was shown that iron man was off rescuing other superheroes instead of "saving the planet," stark industries stock dropped significantly. and then oscorp got all these big contracts, taking away almost all of stark industries' revenue. tony's personal fortune isn't tied up entirely in stark stock, but he definitely took a hit, whereas i'm sure osborn has remained the majority stockholder for his own company, because he's a narcissicist, and has probably multiplied his fortune at least tenfold.