rbmazda3 said:
Could this really be true? And if so...why? (uhm)
Yes, it's true. The main reason is that the firewall has been integrated into the strut towers, so it acts like a built-in tower brace.
If you look at almost any other car, the strut towers are standing alone, a short distance away from the firewall.
If you look at the Mazda3, the firewall extends out to the strut towers and actually connects to them under the two rear-most strut bolts.
That, coupled with numerous under-car cross-members and a host of other updates, has made the Mazda3 one of, if not
the, stiffest cars in its class.
There
are additional braces available for both front and rear but you should only need them if you plan to do some auto-x or if you want to add to your rice-factor. (spin)
Here's a picture of the AutoExe set from Corksport that retails for $577+shipping.
And here's the MazdaSpeed bar for $338:
GT-Spec also makes a whole host of reinforcing struts for this car. The whole kit will run you about $750.