USPS is Pretty Good for Packages, But....

I use USPS.com to ship packages a lot.  I like using USPS.com to ship packages.  It gives me the rate, I pay for it, I put the package in my mailbox, and the service generally provides tracking.  I use Priority Mail a lot for packages, which does provide tracking.  I don't have to take the package to another location, like the horribly customer-unfriendly Kinko's a few miles away.  I don't get suprised by charges later, such as "rural delivery surcharge" and fuel surcharges, like Fedex loves to charge -- after they've quoted me a rate! 

But, still, USPS can improve.  For one thing, you choose a day for your package to go out.  If you choose a date, then your package HAS to go out that day.  If it doesn't go out that day, then you have to void your label that you printed, ask for a refund (which takes 3 weeks), and print out another label.  So why, when the USPS site gives you a choice of days to send your package out, can't they tell you that "Monday is Columbus Day, so you should not choose this date."  Why can't they not offer a postal holiday as a choice when you are shipping a package?  It sure would make things easier for their customers. 

Here's something that just came up today when I tried to order shipping supplies from USPS.com.  Why can't they just let you know upfront that you can't order more than one of these boxes?  Why allow that quantity box to be set by the customer if you aren't going to let him order more than one?