Switching to Mozilla Thunderbird as the main mail app on my iBook gave me some undesirable insights on how Apple tries to constrain choice in internet applications. I assumed that you set your standard web-applications in the system preferences. After searching through them and the entire system afterwards, I was astonished to find the dialog hidden within Apples own web-applications. The standard web browser is set in the Safari preferences, the mail client at the correspondent place in Mail.
This is a change in Apples policy, since older versions of OS-X allowed to change your web apps where you expect it: Among the internet & network options in the system preferences.
Certainly not the Microsoft way in browser bundling, but still a sneaky attempt of preventing people to adopt different products.