Oh ye of  little faith! Joystiq interview: Ironclad talks 4X strategy with Sins of a Solar Empire: "The research tree in Sins approaches the size and quality of a 4X research tree and dwarfs pretty much any RTS game I can think of." 
You may also like the same article's "How does Sins work in diplomacy and espionage, two elements that usually play a fundamental role in 4X titles?" I found it by Googling for "strategy game 4x tech technology tree". I've edited that para to remove the game-specific comparisons since we have such an explicit ref. Since that makes the 2nd and 3rd paras 1-2 sentences each, I've combined them - I also think thet fit together reasonably well, as the high cost of high-tech implies a need for intermediate productivity enhancers. What do you think?
Re the last para of "Tech tree", as I said, I'm happy to remove it provided the refs get transferred to Technology tree first. Done!
I've re-ordered the sub-sections as discussed above.
If you're happy with all that, intro and clean up are next!