Technical leads and architects are back-end developers with broad experience with Drupal. They understand how to analyze and set requirements. They establish the high-level development strategy through module selection and configuration. They focus on sitewide concerns such as integration, scalability, performance, and security.
However, even these highly experienced experts wouldn’t be expected to know everything there is to know about Drupal.
An example: http://groups.drupal.org/node/66638