I agree. The Amiga is the only retro computer that outlived the other retro computers of the 1980-ies and most of the 1990-ies. While there are new software released for Oric and Amstrad, this does not magically turn these machines into alive machines with strong community and new developments. I coded a CPM games two years ago, did this made the CPM alive? If some guy creates an hardware add-on for his Atari Falcon, this does not brings the Atari back to life.
As I use emulators on my Amiga, I have pretty good view of the various retro communities. Surely the Amiga is the most active of them all. While the C-64 is very strong, it is not as much strong as the Amiga. And the Amiga is still a decent useful machine, unlike the C-64 and the Atari ST. All the C-64, Vic-20, Speccy and Oric fans are using PCs or Mac to connect to the Internet and do serious work and post on these forums, while there are people who use their Amigas to post on the forums. I guess this makes the Amiga the only that outlive them all.
Additionally on the Amiga we have - OS wars - AmigaOS 3.9 vs AmigaOS 4.0 vs AROS vs MorphOS. Forum wars - Dammy vs Franko vs Jerkany etc.
Hardware wars - Sam460 vs Pegasos vs old Macs.
New complete hardware configurations - announced and even some of them released - Sam440, Sam460, Natami, AmigaOne X1000.
New versions of the OSes that are not opensourced.
New hardware peripherals for the old machines, created from companies that are on the Amiga market since decades (Individual computers).
Online stores where you can buy Amiga stuff brand new - AmiKit, Vesalia.
Online depositories where you can watch for new releases - Aminet, OS4Depot.net
Active daily updated news sites - Amiga-news.de, PPA.pl.
Bi-monthly paper magazine - Amiga Future.
Several very active forums - AmigaWorld.net, Amiga.org, EAB, LemonAmiga.
Active demoscene that competes with PC releases on main computer scene events.
Old greybeards who come to say hello to the community (Dave Haynie).
Haters - people who went PC long time ago that come to say how much advanced their new machine is compared to our antiques.
Enthusiasts - people who love to play with their Amigas over anything else.
While the other retro machines have some of the above, they are magnitudes smaller than the Amiga.