Personally, I'd say the error message coming up provides far more information than a simple 404 page and may be important if the same error cropped up for someone with their site set up correctly, so taking that information away and providing just a 404 error page could lead to people who do have the correct sitedata folder (or at least, aim to have) not getting debug information to help solve an issue.
Out of interest, what shows for a 'normal user' without debugging enabled? - I would say there is potentially a case to have some kind of 404 page without the debug stack trace for users who do not have debugging enabled, if the alternative is a plain white screen crash as sometimes happens with these 'fatal errors'
For developers, I'd say the debug info is the right way to go, and not a simple 404 page.