And who would "the other ppl" be? There is just NVIDIA with PhysX and Havok. And you can't just walk out into the scene and expect everyone to know your physics engine or even use it in developed games. The games that were using Havok just weren't developed with extensive physics in mind, they always used it in minimal possible way just so they could run even on crappiest dual core.

Just take Painkiller for example. All the physics affected debris and objects just fade away after 5 seconds. But when all the same objects are flying around i couldn't notice any slowdowns. So why not leave them there for 10 minutes so they are affected by any later rocket/grenade launcher or corpses? Or Doom 3 back then. All monsters just evaporated after a second. But when i used a no-evaporation mod, the monsters were flying around corridors, hanging on railways, sliding off slopes etc. Half-Life 2. Stuff faded away much later and i couldn't notice any slowdowns. Ever.

I wonder why they don't implement Havok with different levels of physics detail. So if you have crappy CPU, you can set it to Low. But if you have high end quad, you could set it to High and experience larger amounts of objects be affected by physics.
But now it's just always "ON" with no adjustable levels. So they just bog it down to a very minimum so it works on all systems, starting from crappiest dual cores).