The numerical identification of posts and pages is key information that should be displayed in a column next to the title, number of comments, and so on.

As Justin points out, this information is essential for many WordPress template tags, as well as many plugins and themes. Removing it was a mistake, and leaving it out is just laziness.

The argument that users who need this information should know how to get it is absurd. Perhaps WordPress should stop showing post dates, page titles, and the number of comments for each post, because, after all, anyone who needs that info should know how to get it.