Hey now, that's not completely fair. The US Post office delivers on Saturday (and will deliver it as soon as it arrives, as will FedEx).
Now, UPS... when they say 3 business days, they mean it. Your package could arrive in your city on the morning of the 2nd business day. It will wait there until the third day (FedEX and US Post will send it out as soon as it gets there though). UPS are bastards that way (I'm pretty sure it's a policy. My roommate pointed it out and ever since I've noticed that, it can arrive days earlier, they will *not* deliver it until the day it was promised. I suspect it is to try to encourage you to pay more for the quicker delivery. I guess they feel if they sometimes deliver quicker than promised on "slower" delivery they can't get you to upgrade your delivery option).