This is a difficult post to reply to because it's a mix of common sense, lack of information, and incorrect information.
We need to agree on something before we can have a real conversation about this: Massassi succeeded (at least at some point). (I assume you agree with this since you said I got lucky with massassi.)
So let's talk about Massassi first. I didn't create Massassi with the intention of turning it into a community site. I created it to post some tutorials. I eventually included forums. At this point it was an editing community -- a bunch of people creating addons for JK. However, it didn't get comparable traffic to other JK sites (well, JediKnight.net which was the biggest) until we added levels/addons. So in this sense Massassi didn't succeed because it was a community site, the community grew up around the other aspects of the site (tutorials, which initially were created by me, but eventually there were tons of other authors as well; and levels/mods, which most definitely weren't created by me). So yes of course I was lucky with Massassi. I was lucky that people helped me write tutorials. I was lucky that authors submitted their levels/mods. I was lucky that I had a fleet of unpaid volunteers to help post all the submissions. I was lucky that certain people (spart, for instance) saw value in the content of our site despite the fact that it was ugly as sin. I have never, and will never, contend that Massassi's success was solely the result of my hard work. My hard work over the years is only a fraction of a percent of what it took to make this site awesome. And regardless of what you or other people say, I still say the site was and is awesome.
My opinion is that there needs to be content in order to grow a community in the first place. You say I'm completely wrong and I just got lucky. Please tell me where I went wrong.
Now I'll address your contention that I have failed miserably at every other community-building idea that I've had. Please list for me any other "community building" ideas that I've had and failed at. I can list some SITES I've had that didn't turn out to be very popular. But I contend that these weren't popular because the games they were based on sucked.
Indiana Jones: license prohibited editing, site got quite a lot of traffic and had active forums for a short amount of time (<1 year)
Force Commander: Game sucked. We got quite a bit of traffic for our review and some tech support threads but site failed (duh)
Serious Sam: Was a section of Massassi, got tons of traffic, biggest level/mod db until I stopped working on it, decent traffic on forums, best tutorials and a lot of traffic.
VampireCentral: Good traffic, active forums, got job offer at Gamespy based on this site (couldn't take it because I was in the military at the time), ended up managing PlanetVampire.com for a while on the side but I didn't like the game once it came out so stopped working on it.
SWOnline or something, Justen took it over because I wasn't into the game.
In all these cases I was creating sites based on games. These are obviously going to be short-lived sites with traffic that falls off over time (and people stop playing the game). If you contend that Massassi is the only success of all of these because none of the rest are still around, I call bull****.
I've also worked on the software for a bunch of community sites that I can't list because I'm under NDA. Suffice it to say I worked for a company that serviced non-profits. After my contract was up I was offered a full time job (but didn't take it because I found another job at which I could work from home).
Now we can talk about the forum software I wrote on the side (while commuting back & forth on the ferry to Seattle). I didn't ever have the intention of creating a community with that software, the intention was to sell it. Working on something 2 hours a day for months in addition to my 8 hour a day regular job was too much and I eventually stopped working on it before ever making a public "for sale" site. Call this a failure if you will but I learned a lot about scaling (it could handle > 50 million posts on a single server whereas vb at the time choked at about 5 million on same hardware), I learned a lot about database tuning, etc. You could argue that I never had a chance in hell of selling it even if I did ever finish it. You could be right, *shrug*
So is there anything in particular I missed?