What has been clarified:
https://twitter.com/GabeAul/status/558063018677112832
No. Once upgraded to Windows 10, we will keep it up to date for the supported life of the device, for no additional charge.
I would ask caution on this, as always, it can lead to an understanding that could be similar but different to their.
They need money, so they're gonna find a way to get some, this is where the "extra" come, or maybe from another source (advertising ?)