*edited twice: Here are my reasons as to why (revised):
The reason why I feel so strongly about the dead shrub is because it is an item, just one that can't be added to your inventory without hacking. 'You can't mine it nor craft it' (quoting someone else) is exactly my point. It's generated in desert biomes on new chunks, it's yet one more thing Minecraft has to render, you get nothing when destroying it, and even if you want it for aesthetic purposes, you cannot obtain one legitimately and must build around it.
The dead shrub is the only terrain item that cannot be produced, so if you want it, you'll have to build around it. It's the only purely ornamental object that requires you to cater around it.