"Any customer can have a car painted any colour that he wants so long as it is black." - Henry Ford
We see it all over the web, development companies that create sites in nearly every language and technology. Do they really claim to be experts in everything? How do they find the time to keep up with all the advancements and changes for so many systems?
Whatever platform you choose you want a qualified expert who works with that product on a daily basis. They should know that system inside and out, and be able leverage it's strong suits while avoiding it's pitfalls.
It's important to note that while Drupal is written in PHP they are not one in the same. Drupal development is quite specific as most custom work needs to be integrated into the CMS.
Through experience we've discovered more efficient methods for using and developing Drupal sites. This means we complete projects in less time and at a lower cost than others.
We intentionally limit ourselves to our core competence. Drupal is what we do everyday, and what we do best. If you expect the best, call the best.