This isn't worth studying for the simple minded. AlexanderBlade has said that a few times, but he's mostly wrong. What he probably means is all symbol names are lost (variables, functions, structures). Scocl is also such a broken compiler you'll end up with garbage decompiled code anyway. Cleaning that up is cumbersome, but it's logically valid.
The part you said about "you cannot decrypt even if you decompress" is nonsense. The crypto and compression is well documented. Things don't magically get deleted, otherwise the GTA engine wouldn't be able to interpret the byte code.