No it doesn’t. You need a subscription only if you want a paid support. More info to come next days.
Yes, it’s almost the same (it just contains a couple of extra modules) and it can be downloaded only if you became a Nethesis reseller. This is why the community proposed the subscription above.
If you’re interested, I can give you commercial contacts in a private message.
If you use the community version you can choose whatever you want between SOGo and WebTop (or even Horde!). The community is very quick on giving support and fixing issues!
By the way, if you want to buy the Enterprise version, only WebTop is supported there
If you need more info, just ask!