In short: the datetime attribute (on both del and ins elements) should permit just a date value, in addition to permitting explicit dates with times.
Reasoning/advantages provided on the wiki: http://wiki.whatwg.org/wiki/Del_element I encourage fellow web authors to add opinions/comments to that wiki page. Thanks! Tantek -- http://tantek.com/ I made an HTML5 tutorial video/book! http://tantek.com/html5