Product description history and HTML "diffing" of articles has been (re)introduced. Moderators and contributors alike can look at the history of product descriptions and use a nifty diffing tool (thanks to Daisy Diff for the backend).
To access this functionality, have a look at a product's history tab (eg: http://www.productwiki.com/sanyo-xacti-vpc-hd1000/history/) and click on the "compare versions" link. This brings you to a list of the changes to the product report's description, with the ability to look at previous, or compare versions using the diffing tool. It is done in a similar way to Wikipedia.
Have a look at this example, comparing subsequent versions of the description. The new edits are in green and the old edits are in red. You can use your keyboard's left and right arrows to cycle through the edits one-by-one.