Man, I think that if they're not cheating then they're bragging undeservedly (i.e., they're making it up.)
I just finished testing your assertion that you can get a science win by turn 200 -- bottom line: it didn't happen. I was India, immortal, on a large continents map, had an almost perfect start -- coastal river, 2 wheats, a cow I think, 2 golds, a couple of fish, 2 sugars, lots of riverside grassland + a deer & lots of nice hills. 2nd - 4th city locations also optimum for growth. Ran the Tradition tree, then half of Rationalism & half of Freedom + eventually the Patronage opener. Anyway, my pop (& thus science) shot up super fast and I was the tech leader for quite awhile. Managed to build GL at turn 41 & took CS; also built HS & used the GE to rush the PT & then used the PT GS to bulb Astronomy. Once I had PT & Rationalism then I spammed RAs. On a large map the science should be easier than on a standard map, shouldn't it? All the AI civs but my next-door neighbor Washington were friendly throughout, and I had max RAs active the entire game (done correctly I might add).
Anyway, at turn 200 I had just finished Steam Power, had 4 GS saved and 2 on the way (within 20-30 turns or so), 6 or 7 active RAs pointed up my tech tree to Nano -- which was still too far away to start the bulbing party. Finally started the bulbing party at turn 245, with 1 GS + Oxford + a couple of RAs still to come shortly. Immediately put Delhi on

focus & built Apollo + spaceship factory; built spaceship factory in the 2nd most productive city & just built boosters in two other cities. Bottom line: Finished the spaceship at turn 275 (with an unsatisfying Charlemagne score).
So, I think this game was pretty much optimum, and I played damned well if not perfectly. So why didn't I come even close to winning by turn 200?? Yeah, I could have started my bulbing party 10-15 turns earlier since it turns out that 2 RAs popped after I already had Nano & they gave me umpteen thousand points toward the Nuclear Science path.