Actually, there's a lot more to it that can change the performance.
First, there are opcode caches, which can significantly boost the performance of dynamic code. For some reason, not every host is running them... But in the case of the opcode cache, it removes PHP having to dynamically process through the php file, and 'generate' the code for execution, then execute it.
Second, there are various caching systems, both at the server level (like memcached), the program level (wp-cache), and the sql level (mysql's query caching). Each of them can significantly change the loading time depending on how they are set up. There is also the 'object cache' of WP2, which effectively tries to cache the results of certain specific queries on the webserver end (which, depending on the architecture of your hosting box(es), typically will not make any useful performance difference..).
WP-Cache in particular is one thing everyone has in their control (rather than the host's control), and is the closest thing to delivering static pages back. The difference is that apache still has to start up php, and the wp code has to load far enough to trigger wp-cache, and wp-cache has to decide whether the requested page is in its cache... etc.
However, it has been shown (in other discussions) that well-configured systems using a combination of caching and performance tuning can deliver millions of hits a day under WP/PHP.
Anyway, just wanted to make sure it's understood that it's much more complex than simply "PHP vs HTML", that there are 'intermediate' stages along the way.
Oh yeah, AND the webserver software being used (i.e., apache, iis, lighttpd, thttpd, etc.) also significantly impacts performance of heavy sites, PHP or otherwise. In fact, if a lot of a given site IS static information (CSS, graphics, JS, etc), and not WP PHP code, then a number of alternative webservers could make huge performance differences -- if you are hosting yourself and can change webserver apps! ;)