......But 30x40 *is* one of the Limited Time Promotion sizes..... and his regular print shows that size available...
Like Adam, I've encountered the same thing before but didn't bother asking about it. For whatever reason, the code for limited time promotions doesn't use the same resolution calculation for available sizes that regular prints do.
i.e. you need a higher resolution file to to print the same size canvas print if it's a limited time promotion versus a regular canvas print which seems strange...