Gary Price :
Yes all computers running windows 7 and 8 can be upgraded to 10. From the sounds of it Microsoft is willing to give windows 10 to windows 7 and windows 8 users for free for 1 year.
No it's free upgrade to windows 7 and 8/8.1 for the life of their machine if purchased within a year of the release date. The for year means it has to be acquired with the first year.
Costs:
All updates to Windows 10 are free.
If you purchase in the first year you won't ever have to pay for Windows 10 on that machine
If you wait till after the year and purchase there will be a cost which hasn't been announced yet but after the ontime cost updates will be free for entire life of machine.
I'm not sure how MS will do it if you need to reinstall they OS but I'm sure if you have a legal license you will get Windows 10 for free even after the year.