I have 4 Win7 home premium/Win8.1 home+pro laptops and 1 Win8.1 home tablet, and my parents have 2 Win7 home premium laptops, I upgrade them all smoothly. But later I found all the new Win10 systems have different minor issues. I manually fixed some, and Microsoft released hotfixes for some others. At this time the only issue I have is on one system search "settings" does not return anything.
So my opinion is: there might be something there, it's just you didn't see them yet.
Still I respect Microsoft for doing a good job on upgrading old systems to Win10, it's quite difficult.