But why would you set your aim for something that difficult right off the bat? If you can't make it work now it's a very bad idea to assume that you can probably make it work later. If it turns out the "next generation" you're waiting for isn't gonna be around for another 6 months, are you just gonna sit tight and wait?..
First of all, don't base your plans on what other people have accomplished unless you've actually figured out how they did it.
Yes, they had a better physics engine. They might have managed to use Bullet natively, but rather than that, I would guess they just made their own custom physics engine made especially for their game, for optimal performance.
Exactly. If you made a game with just spheres, who gives a crap about any other collisions. So an optimized physics engine built around sphere vs sphere dynamics would run many times of magnitude faster than the varied, catch all, accurate physics of jBullet. It could be they turned the sampling rate waaaaay down too. You could do this in jME's bullet too, by lowering the accuracy variable, but I think it's more of a matter of getting it running on the device in the first place. But I mean, think about how many "Man behind the curtain" moments there are in gaming to pull off crazy effects. Half of the time they do something in such a way so that it's way faster than it should be, but maybe only works for 90% of the viewing angles. So what do they do? Ensure the player never sees that 10%! :p Gaming pre-2000 ish relied heavily on this to achieve "the next big thing." This is still in practice today. The only difference is as computer speeds increase, the need to half-ass, or clooge things, has gone down because we have the raw horsepower to throw at it.
I mean hell, the final boss of Doom2 is really that famous sprite model of John Romero's head behind the giant skull boss's head. Why'd they do this? No one really knows, but I could bet it's because they didn't want to rewrite the walldef collision codes to REALLY do what they wanted. Instead, they did what worked, and figured the casual player would never know they clooged it :p
Man, to this day I still use tricks that I learned back in Doom/Quake level design. Teaching since 1995 :p
Digressing topics weeeeee :p