From a development-plan point of view, we did this new work not only to increase a standards score, but because it was based on real customer demand. Customers asked us to rationalize our margin and padding models. We added these were features because there was a need. This determines whether the extra spaces in the content are shown or collapsed. One of the central notions we have is that if you can set a property, you can set it dynamically.
Any property can change over time.
The white-space property turns out to have some really bad effects on performance and predictability if you can change it over time, because of its interaction with HTML compatibility and parsing rules. We decided that it was lower priority than other work that we needed to do. Over time, we'll look at the requests we receive for CSS1 and other standards support, and our support will grow. As mentioned above, requirements we get from intranet users tend to be prioritized differently. They want to make the browser a rich client for working applications.