Apples and Chicken Noodle Soup. Personally, there is no comparison to the broader gaming industry and HTC.
This game attracts a unique breed, which the majority participate because of the personalities involved, the long term relations across the globe, the camaraderie, and the game/social atmosphere that simply does not exist in WoW, Quake, Call of Duty and the other like minded twitch games.
We tend to be older, historically interested, financially invested in ways that differ from the main stream norm. By invested I mean in real, tangible things. It's one thing to have mom buy you the latest and greates Xbox, but us, with families, lives, careers, and so many other things going on, we still chose to invest our time with those we have known for so many years. Many of us have been around this community as a whole since the early and mid 90s, some far longer than that. That is an investment in a lifestyle, not a console.
Consider the complexity you mentioned. Imagine, if you will, the precision that the dogfight requires to hit the target. Can World of Warcraft do this? No. The game is "close" you select a target and can jump around, run, wiggle and do what you will but the targeting is either in front of you or behind you, and no precision is required. Stutters, stalls, lag, all absolutely irrelevent as it doesn't matter if you lag for 3 seconds, you come back and your target registers the damage. You cannot achieve the level of precision this game requires and back it up with a complex model, it will fail. 3 Second lag in a dogfight means you warped 4 plane lengths away. But, the game is far more "complex" with it's battle grounds, economy, tiers and the like. Technology for the main stream just simply does not exist to have this much complexity and graphics load not cause a delay which is absolutely unacceptable in this type of game, and frankly would render the game unplayable. Many games have far superior graphics. Let's look at Microsoft Flight Sim X. Stunning, my system maxed out has unbelievable graphics. Put 10 people in the flight and we all best be cramming our graphics down. Put 150/200 into a scenario with animated bombs, explosions, smoke, and all of the other things that MSFS x does not offer and the game dies. Complex, yes, extremely limited, absolutely.
So, the complexity is now in the hands, and imagination, of the players. In this game, you literally get out what you put in. You can chose to immerse yourself in a full blown scenario and fly a coordinated mission with a hundred players from across the globe or dogfight 1v1 in the DA, and anything in between. Adding gimmicks, tricks, leveling, questing options reduces a highly specialized game down the level level of a broad based market such as the likes of WoW, Starcraft, Call of Duty and the like.
Adding something "addictive" to a game that has evolved because of the players involvement and not some marketing arm trying to generate sales is counter productive to what attracts a niche player to this game in the first place. One might argue, HTC could sell more subscriptions but lose the base that built the game due to the deliberate avoidance of said marketing schemes and gimmicks.
The saving grace is, HTC is one of us, flew the games, knows the games, plays the games, yet builds One Game and One Game Only. Don't be quick to assume HTC doesn't know what he Could Do, be grateful he chooses not to. The subscriptions could grow but the game would die as we know it. Once you start building towards the twitch crowd, you have to introduce new and improved daily or lose their interest. We have, as the core player base, people who used to play flight sims when you could count the pixels on the wings, and still pulled off some of the most memorable special events in history. But then, more was put into them at the time as well, more "personality" and less "complexity".
How HTC keeps the 2 weekers is simple. Do what is being done. Some times you just won't keep them all, but you will keep those like minded players, who will be the long term subscribers which will increase your base.
One old farts point of view.