Deleted pages are never truly deleted. A more accurate description would be "hidden", and there are different levels to which a page can be hidden:

* Blanking a page, or part of a page, is an action that any editor can perform, and any editor can undo. This hides content from the "live" page, but anyone can view the blanked content by looking in the page's history. * Deleting a page is an action limited to administrators, and similarly, only an admin can undelete a page. A deleted page is basically treated by MediaWiki like it doesn't exist, and only admins can view the deleted content. Individual edits can also be deleted, but this is not as common. * Lastly, oversighting can be used to hide content from even admins. Admins can oversight stuff as well, and in these cases, the oversighted content can be viewed by other admins, though it requires more work than viewing deleted stuff. For oversighted content to be hidden even from admins, the oversighting must be done by another user group called (aptly enough) oversighters. In the context of WMF project, entry to this usergroup is tightly controlled (seriously, it makes the request for adminship process look like an open door), and anyone selected for the role must personally confirm their identity to the WMF.

The main point is that, in all of these cases, the content is never gone, but simply hidden; the MediaWiki software is designed so that every action is logged and can be reversed.

That's not why stuff gets deleted from wikipedia, the USERS do that, because they have processes and policies which encourage it. That's a much more difficult problem to address, because you can't fix it with technology. Same problem affects a redesign... That said, I have seen some encouraging evidence that the community wants to address the usability of the tools and UI on wikipedia, and the engineers working at the foundation have their own ideas which are a little more realistic, for example:

http://www.mediawiki.org/wiki/Athena

It is also a disservice to the entire editorial platform if they can't pay their own bills and go under. Or if they overload their servers to the point that people complain that "Wikipedia is always down" and migrate to one of the less free alternatives.