Big Savings
On A List Apart, Daniel M. Frommelt describes how he rewrote a static copy of the Slashdot front page using current web standards. This is a great example of the amount of money a high-traffic site can save with a standard-compliant design:
Most Slashdot visitors would have the CSS file cached, so we could ballpark the daily savings at ~10 GB bandwidth. A high volume of bandwidth from an ISP could be anywhere from $1 - $5 cost per GB of transfer, but let's calculate it at $1 per GB for an entire year. For this example, the total yearly savings for Slashdot would be: $3,650!
Remember: this calculation is based on the number of pages served as of 13 June, 2000. I believe that Slashdot’s traffic is much heavier now, but even using this three-year-old figure, the money saved is impressive.