It's also the thinking that got us Doom. ;) There are use cases where performance trumps security; the only issue here is that "multi-app semi-trusted computing environment" isn't one of them.
On a related note: Doom apparently does contribute to security proof of concepts though. http://www.techtimes.com/articles/15606/20140916/security-ex...
Which makes me wonder if the non-clearing memory issue exists for the printer's video driver and whether that could be used to retrieve something like a saved password or ssh key.