Office has a huge amount of legacy. I get that porting it to iOS had to be done. Microsoft provides Office for the Mac desktop. But porting to Android is a whole other story. Porting it to Android validates Android as a platform like nothing else. It'd be equivalent to Oracle releasing their DB server for Linux way back in the day, it gave the platform instant enterprise-cred whereas before it really only had hacker-cred and FOSS evangelist support despite the knowledge that IBM was spending a whole bunch of money on it internally.

You're right that Nokia has a track record of supporting and developing across multiple OSs but how has this turned out for them in the long run?

Samsung are right to keep their options open but I think they should go the Amazon/Nokia route and differentiate on top of Android. Having said that Samsung is probably more than large enough and has a large enough R&D budget to pursue multiple strategies.

It's really hard to see how this plays out. I thought we'd never ever see the day when Microsoft developed for Linux or Android unless as a bridge to their own world. I thought past history, pride, lack of trust, wrong momentum, or whatever would stymie them from making the transition. If I were a beige box manufacturer I would be extremely concerned that the Microsoft may move on from phones and tablets to laptops or even PCs, now that hell has frozen over you never know what they might do.