Why is the tree one of the hardest things to get right in 3d games?

[A Black Falcon]

I think trees are inherently more complex than other things, like buildings and cars. However, I've seen plenty of games that do trees right, but rarely in racing games.

Very rarely. The only decent trees you see are in some FPSes, and even there it's usually some trees, not all trees...

In PGR3, for instance, I have a suspicion that those trees wouldn't look quite as nice as they do if they weren't blurry...

How DO they get the sheep to eat the grass so evenly?

Or goats. :)

Generally, structures humans build are constructed to look attractive to other humans or with simple geometry in mind so the physics is easier to work with, so they are easier to render thanks to all that. But, there are a few things that are pretty wiggy... Like, destroyed structures. Generally every destroyed building I've ever seen looks like it's supposed to look like that.

Often true...