The trade off they're talking about is to arrive at the same end product.
The reason games are typically released as "fetuses" is because it reduces the financial risk. Much like any product, you want to get it to market as soon as is sensible in order to see if it's worth continuing to spend time and money on it.
I found "This New Ocean" by William E. Burrows to be a rather good account of the first space race, as it covers both sides in an equal amount of detail.
The content, e.g. quests, map, npcs, dialog, etc are all in proprietary formats (Runescript and various config formats) but this doesn't compile to Java - it's simply loaded by the engine.
The engine, server and client, is 100% hand coded in Java, and the client portion of that is what we manually 'ported' to Javascript. I say 'ported' in quotes, as though lots of the new code performs the same or similar job to the existing Java client (bugs and all!), its implementation is sometimes quite different to that of the original Java version.
The reason games are typically released as "fetuses" is because it reduces the financial risk. Much like any product, you want to get it to market as soon as is sensible in order to see if it's worth continuing to spend time and money on it.