I'm wondering if http://www.google.com/search?q=%22the+presence+of+absence+of%22
is a list of typos or whether the phrase "the presence of absence of X" means "the presence of Y where Y is the absence of X". This phrase also occurs in the disclaimers of Creative Commons licenses: http://creativecommons.org/licenses/by/3.0/legalcode
"Unless otherwise mutually agreed to by the parties in writing, licensor offers the work as-is and makes no representations or warranties of any kind concerning the work, express, implied, statutory or otherwise, including, without limitation, warranties of title, merchantibility, fitness for a particular purpose, noninfringement, or the absence of latent or other defects, accuracy, or the presence of absence of errors, whether or not discoverable. some jurisdictions do not allow the exclusion of implied warranties, so such exclusion may not apply to you."
If it's a typo, it doesn't make sense to disclaim the presence or absence of errors. It's difficult to ensure the absence of errors, so the license must disclaim it to avoid trouble later, but it is really easy to ensure the presence of errors, so it makes no sense to disclaim it.
If it's not a typo, why can't the license just disclaim the absence of errors? Someone in Freenode #fsf channel told me, "That would make too much sense."