Why did BitcoinEXpress plan a 51% attack on Namecoin? I don't understand this post.

What is "ArtForz modified exploit"?

What does "Gavin's patch will not work for the exchanges" mean?

Any more important details I'm missing?
This post by ArtForz on the forums explains the attack:

https://bitcointalk.org/index.php?topic=43692.msg521772#msg521772

Quote: "By exploiting the fact that retargeting ignores one block interval every period, it's possible for an attackers' fork chain to "jump backwards in time" and create lots of blocks at low difficulty without running nTime off into the far future."

This attack has been proven to work on GeistGeld (which uses 10 second blocks and 16 block retarget intervals). It was rather easy there, because of the low intervals and because the developers "forgot" to adjust other constants regarding timing and clocks. They since made it much better.

Now it seems it will be tried on namecoin, with the goal of making bitcoin more secure.