There was an announcement last week that the WTC might be rebuilt as four 50 story buildings instead of two 110 story ones. That would put the towers no higher than surrounding buildings and make them less a target. It'd also make it easier to evacuate in an emergency. Really tall buildings like the twin WTC towers only make economic sense when you're taking about places with incredibly high real estate costs and limited availability.

I was on my way to work when I first heard a plane had hit the WTC. Being an aviation history buff, I thought it was an accident like that B-25 crash. However, as soon as I saw the photos of clear skies, I knew it wasn't an accident. That B-25 was only on a short flight and was approaching its destination, it was probably only carrying 100-200 gallons of gasoline when it hit. Based on that, it probably weighed no more than 26,000 pounds and was probably only going 200 MPH or less at impact. By contrast, those 767s were fueled for a transcontinental flight and had taken off shortly before impact. I'd estimate they were probably carrying 10,000-15,000 gallons of jet fuel at impact. That means they probably weighed over 300,000 pounds and were doing somewhere around 300-400 MPH at impact. It'd be very tough to construct any tall building that could withstand those impact forces followed by so much burning fuel. Water alone isn't enough to put out burning jet fuel, and any fire suppression system would have to be able to withstand the impact so it could function.

http://www.b25.net/#specifications
http://www.boeing.com/commercial/767-200/product.html