Bowie was a musical genius, but he was also a vampire for inspiration, sucking up influences from people as diverse as Dylan, Hunter/Mott the Hoople, Marc Bolan, Lou Reed/Velvets, Iggy/Stooges, Phillysound, Robert Fripp, Kraftwerk, Chic and Scott Walker (uncannily on my office Brennan B2 as I write this!). Most likely, all of Iggy's albums together achieved less sales than Bowie's Let's Dance (which had China Girl on it), Herr Osterberg could certainly use the royalties at the time. Those late 70ies "comeback" albums of Iggy have Bowie's production and songwriting written all over them, they are dead ringers to Bowie's Berlin output of the time, albeit more accessible, Bowie obviously kept the toally off-the-wall stuff for himself or James O. didn't want to do it.
Iggy and Bowie rubbed off on each other and both profitted from it. Iggy's ingenious rhythm section of the Sales Bros would later be 50% of the great Tin Machine, to my mind still Bowie's most criminally underrated project. And Tin Machine had quite a bit of Iggy influence in it too.