Bianca Bosker, writing for The Huffington Post:
In the fall of 2009, several months before Apple approached Siri, Verizon had signed a deal with the startup to make Siri a default app on all Android phones set to launch in the new year. When Apple swooped in to buy Siri, it insisted on making the assistant exclusive to Apple devices, and nixed the Verizon deal. In the process, it narrowly avoided seeing Siri become a selling point for smartphones powered by its biggest rival, Google. (Somewhere in the vaults of the wireless giant, there are unreleased commercials touting Siri as an Android add-on.)
Its first and only app had barely been available for two full months. And now Siri – and its future – belonged to Apple.
Interesting read on Siri's origins, especially the Android-exclusive bit.
The irony here is that everything I've read says that Google Now is more accurate and feature-complete than Siri at this point. Apple really needs to work on improving Siri, and possibly consider opening up her (?) APIs to developers. (That's what she said.)