Quote: "Spare me your belittlement, I've worked with enough engines to understand the concept and differences between physics engines, game engines, etc. Any engine worth its salt is modular and the parts can be swapped out."
avoid the real question and respond to an off-comment; gives me all the answer i'd need on the subject.
Making an engine that is modular enough to support PhysX or Havok, is like making one that supports OpenGL or DirectX as the renderer, or supporting multiple base platforms like Wii, 360, PS3 and Windows.
Especially as the base formats supported by both are quite wildly different and propriotry.
You have to trade off features, performance and/or development time in order to incorporate all of that. Why the hell do you think more and more companies are using middleware now.. takes the pain out of most of the choices they make, as it's already being worked on fulltime by someone else.
So all you have to do is come in an give it a bit of fluff and some more specific features to what you're working on at that point.
Source has *only just* become multi-platform compilable, and right now this is only Windows and 360. They have yet to support Wii, Mac and PS3 isn't due for a few more months.
Simple fact of development, unless you're a specific middleware developer you have to make those sacrifices. It is quite rare for an actual game development team produces an engine specifically designed to not just be modified but have entire components replaced quickly and easily with the minimal of fuss?
That's an achievement, and if you actually believe that this is something common-place for engine development then I feel really sorry for you.