Why isn't this supposed date on their website then?
That is because there is no release date available. The hearsay of a sales rep at Cingular is not proof of anything, especially a release date. Sales reps likely have no more information than you would, and with the NDC's involved they will most likely not be able to release any info prior. The date given (June 11, start of the WWDC) is probably the date when the sales reps will be given the information and correct sale and release date, not the actual release date itself.
This story tells and proves nothing. The sales rep more or less told the caller in that story to wait until the WWDC to get more information.
So... again.... nobody will know anything until the WWDC comes around on June 11, so don't get your hopes up just yet.
Pay no attention to the rumor sites, they never know anymore than you do.