With a website, you can totally change the information within minutes.
Can you think of any other medium that you can change your information in minutes?
You've sold out of the most popular products or you've just got a new order in, no matter what you want to change or add, it's done quickly with a website.
The new order has come through but prices have skyrocketed. You can update your product prices the minute you need to.
Your main supplier has gone on holidays and you can't get their products for three weeks. Inform your web customers of the slight delay or offer an alternative product for the next three weeks. What you include is totally up to you.