WSUS is the service... it runs on a server and gets its updates from Microsoft then other computer log into that server to collect their updates
the point is that these computers are not going to the internet {and therefore Microsoft} themselves and you can control which updates are used i.e, filter out the busted ones
anyone can run a update server on Hyper-v (which is free) and you don't need a GPO but that is the normal way... computers can get their updates from Microsoft and the local WSUS (they are both the same updates) but only WSUS can be filtered before download... if you get updates dirrect from Microsoft you can uninstall them again and you can decide that you don't want any updates but only a WSUS allows you pick which updates to install per system so for example the W7 computer may not want sp2 because it breaks their printer drivers
yes home and pro can both use a WSUS but most people think its only Pro because Home doesn't really use GPO which as we said is the normal system
WSUS for Windows 7 will need extra work to set up because Windows 10 uses a different network system... in practice most people keep Windows 7 computers on a different network to Windows 10 so that Windows 10 doesn't bugger up your 7 network but it is possile to run them together i.e, WSUS for XP Vista and 7 then a different W10 Wsus is better than one WSUS for everyone