IO540, not sure how you are measuring the size of the page, but the HTML on a typical PPRuNe page is about 60-80K. Before I posted on it, the last page of this thread is 57K. That is pretty similar to the Toyota site. So whilst I agree that the HTML behind a PPRuNe page could be tightened up, I don't think it is HTML byte count that is making the other site faster.
It probably isn't the low volume of users either, at least not right now (2:30am), though that would make a big difference when PPRuNe gets busy during the day. My guess is that the connectivity of their server is better than the current PPRuNe one, but we can't know for sure.
Unless the previous page was the result of a form submission then the backspace key in my browser works (to take you back a page) instantly on PPRuNe too.