Hi,
Regarding checkpoint 6.3 of WCAG 1.0, the associated techniques refer to scripts essentially (http://www.w3.org/TR/WAI-WEBCONTENT-TECHS/#tech-scripts). Also, in the checklist (http://www.w3.org/TR/WCAG10/full-checklist.html), checkpoint 6.3 lives under the section "and if you use applets and scripts". No mention to cookies there.
Anyhow, since WCAG version 2.0 are out since december 2008 (http://www.w3.org/TR/WCAG20/), I recommend to refer to this newer version instead. WCAG 2.0 pretends to be technology independent to ensure its applicability as technologies evolve (and therefore is much less strict regarding javascript and applet for example).
