I don't want to thread-jack any more, so I'll throw my post in a spoiler in case anyone wants to read it or whatever.
[sblock]
...
I'm fully aware that the above metaphor will be incomprehensible to anybody who did NOT program in Visual Basic and C++ during the 90s and early "naughts," but there it is just the same.
As someone who has dabbled in programming myself, I fully understand your metafore. Heck; I've got a better one (still in programming-speak, and speaking only on the mechanics, and not the flavor, as flavortext is mutable in both systems): 4E is Visual Basic; 3E is Assembly.
In 4E, everything is simple, and you can do most anything. Its also easier to do most things the system was intended to do. The game system is a high-quality game system, and has few flaws conversion-issues aside. 4E games that I have seen (when run whole heartedly) are just as good as 3E games.
But with 3E, you can do anything. No matter how obscure, it can be done. It takes 10x the work, and you get out the quality you put in and no more. (Bad Ruleset? Bad game; Bad math? Bad game) But, anything is possible. It is also possible to bring 4E mechanics to 3E, but not always vice-versa. 4E cannot bring more realism into the game, because healing surges let you fully recover from a 200' fall without magic in 5 minutes. 3E can drop realism if it wants.
The difference I see is that, as Kerrick noted, 3E is familiar to people, and they know it has a good following and community support. I know with the economy being as it is, money is an issue; Sticking with a system you can use for any game idea seems like a better choice than buying another game book set just for fantasy RP.
4E has less realism, a turn off to those who enjoy that kind of thing. 3E also has a wealth of sourcebooks/settings/supplements right now.
4E seems to be designed to function better long term (so long as they stay on top of power-creep the best they can) balance and mechanics-wise. 3E needed years and numerous source books to patch unbalances in the game (Try playing a fighter type without access to Complete Warrior or Tome of Battle and see how much you matter post level 10) to make the game fun and fair for all archtypes.
4E is simple, right to the point, and fair for whatever concept you run with it.
I loved 3E for all the neat things that it does. Back when I wanted a ruleset for game idea X, it was there, and it was better than anything else.
I love 4E because, as an experienced DM that I am now, It lets me do anything I want to do with the minimum wasted effort.
[/sblock]
Now, to get back on topic (unless this discussion decides to continue; perhaps it needs it's own thread, like "4E/3E Debate/Discussion" or whatever), U_K! Any ETA on Godsend? (or still more pre-writing on 4E stuff?) Dante's frothing at the mouth and I also want to see some more 3E mechanics for Timelords smashing universes in their bare omni-dimensional hands.