In beta terrain generation was epic. Overhangs here, overhangs there, overhangs everywhere! Look at this lovely skyscraping forest for instance:-

Cool, right?

Now, look at this full-release 1.8 picture of a forest :-

Boorrrriiiinnnngggg, right?!

Now, why cant Mojang just add in the terrain in picture 1?

1) My CPU will explode or something

If you have a CPU like mine and you cant even go near massive structures (In SP and MP) them it'll explode or something crazy like that. Great.

2) LAAG
If you have a computer like mine, and you cant even go near massive Terrain Gen, then the computer freezes and minecraft crashes. Great.

3) Bugs & Crashes
There'll probobly be a bug where if two pigs fall off a cliff at the same time and die at the same time minecraft deletes system 32. Great.