I noticed that rear of the strut tower top is connected by a small black steel part with a crossbeam that runs in front of the firewall, but obscured by the air ventilation intake and wipers motor under the windshield. I noticed the same solution, but stronger in my RAV4. On the other hand, Corolla has rear of the strut towers welded to a similar U-shaped crossmember that also serves as bottom of air intake. I'm not saying it cannot be improved, but strut towers do not seem to be floating free in Toyota cars. Edit: sorry, the title should read "does prius have..."
2010 models don't have any reinforcement between the two front strut towers in the engine compartment. I'm not sure what you're seeing. I've installed a Tanabe strut tower bar, which runs forward and just ahead of the wiper tray. I didn't find anything connecting the two towers at the strut mounts. Can you post a picture? Did you buy this vehicle new or used?
I didn't say the struts were connected directly. This is OEM. See the pictures of the passenger side. The other side is too crowded to take a picture. Sorry for the delay, today is the first sunny day in this Isaac week.
The tops of the strut towers are close to the firewall, so the firewall helps minimize relative motion. Other cars' strut tower tops are further forward on the body. The Tanabe brace locks the towers together and limits forward body flex/twist.
