[astrodust]

My address is particularly important when a package is being shipped, but I can't recall ever being asked to type it in twice in a row.

[tjoff]

Then again, you can do a lot of mistakes when typing your shipping address and it will still get through. It is also easier to spot mistakes since a shipping address contain regular words which isn't as common with email addresses.

One char wrong and your email is completely worthless, and with it your only real link with the service is cut off - often with no way of fixing it.

[eli]

Email is arguably still more important. They want to be able to contact you if the package cannot be delivered.