Some people say that Drupal, in general, is faster(requests per second) than WordPress. I want to know why Drupal is faster. Is it faster because of its cache, sql query or something else?
I see a benchmark here http://sven.webiny.com/benchmark-webiny-vs-wordpress-vs-drupal-vs-joomla-vs-tomatocms/
It's almost impossible to meaningfully compare the performance of Drupal and Wordpress, because their speed varies widely depending on the configuration and installed modules / plugins. Both are capable of scaling when sites are built by skilled developers.
Regarding the Webiny benchmark, it's almost certain that Drupal's page cache was disabled (the default setting) for the test; I ran the same ab command on an Amazon micro instance and got over 100 requests per second.
That said, the Drupal community has a lot of interest in performance (the High Performance group is a good place to start). The core development workflow has a process to account for performance issues. And the ecosystem offers a range of modules to scale even further, including support for memcached, boost, varnish, APC, MongoDB, CDNs, and others.
Drupal definitely has a leg up in the ability to scale with performance and build upon the core technology. It's framework is more flexible because developers need it to be and are usually more interested, as Dylan mentioned. Wordpress is faster out of the gate because its users wouldn't really know how to improve it because they don't need to. They aren't interested as much in the best performance, which fits the platform design and use case. I wrote a blog about performance if you want more information
