6 to 8 weeks

What is up with the ubiquity of “allow 6 to 8 weeks for delivery?” It’s standard on all TV-direct advertising, but also on magazine subscriptions, as I found out recently. Perhaps this is something they cover in marketing classes. The best explanation I can come up with is that it take 6-8 weeks for you to completely forget that you bought something, so that when it finally arrives you are overjoyed at the unexpected blessing of your ginzu knife set/julienne fry maker/Foreman grill/subscription to the New Yorker.