Of course, everyday consumers may not be heavy Office (Mobile) users, but a huge thrust of Microsoft's vision for the platform is into enterprise, as quoted here, so a fully functional and official Office version was a prerequisite.
Here's my Start screen this morning on one of my Windows 10 Mobile test devices, and then checking the Store:
And here's the same set of tiles after the updates:
You'll see that all three Office applications have now dropped the 'Preview' in their names. These universal applications have been fairly mature for a while, to be honest, since they've also been tried and tested on the desktop/tablet, so it's not entirely clear why it took Microsoft so long to drop the 'Preview' tag. (Mind you, Google Navigation has been in 'beta' now for a decade, so who knows what goes on in these big companies!)