Re: What reason is there to upgrade from Windows 7?
There is no new version of Windows after 10 as after that point you are on a continuous free upgrade path, you will just get the latest set of updates.
Windows after 10 is a service as MS want to use it as a vehicle to sell their other products such as Bing, Azure, Office 365, etc.
Also because in the first 12 months after release users of Windows 7, 8, 8.1 get a free upgrade to Windows 10 and then the continuous updates thereafter, why would you not upgrade. If you wait beyond the free upgrade Window of 12 months from W10 launch you will have to buy that last version of Windows. So I expect everyone on those three O/S versions will upgrade to 10 and it will only be the diehard XP and Vista users who really need to think about it. Don't forget also, each subsequent realease beyond Windows Vista has been much lighter weight than its predecessor so you won't suffer a slow PC if you upgrade, in fact it will run much better and will actually be much more secure.
This is why they are predicting a billion Windows 10 users. Also XBox one will be automatically updated to Windows 10 so that will bring in additional users and all the Windows Phone base can upgrade as well to 10 so it will be easy to hit 1 billion.
Biting the hand that feeds IT
