Samsung may be tempted to fork Android, but this will mean no Google Play (in addition to no Google Maps and others), and Samsung is incapable of growing an ecosystem of developers and apps around their platform the size of Google Play.
Microsoft, Apple and Google have this in their DNA. Phone manufacturers, like Nokia and Samsung don't. If they could have build their own Android / their own Google Play, they would have done so already.
On the other hand, it is easier to walk a well-worn path, especially with money in hand. Samsung has the best hand here. Reading http://communities-dominate.blogs.com/brands/2012/08/smartph..., it has 30% of the world market for smartphones. The big problem would not be replacing Google Play, but replacing Google Maps and, to a lesser extent, GMail. In the current climate, one would not think it, but I do not rule out reading a 'Samsung and Apple collaborate in mapping' or 'Samsung and Microsoft collaborate in mapping' headline in a few years time.
Also, companies can mutate 'their DNA'; it is not frozen at birth. For example, the Tabulating Machines Company (nowadays called IBM) has reinvented itself several times, and Nintendo started as a manufacturer of playing cards, and DSM (http://en.wikipedia.org/wiki/DSM_(company)) started life as 'The State Mines' and mined coal, but now is, quoting their site "a global science-based company active in health, nutrition and materials".