What is a letter?
When you submit using the online form, your submission goes directly into the CRM database and is handled (or the ball dropped) from there. Emails are forwarded to the database, but that takes human intervention and time. Paper has to be scanned in and then manually entered, taking even more time.
Wiring letters to CEO's and other senior officials takes even more time because the mail room clerk who sorts the wheat from the chaff has to figure out where your letter goes to be scanned and classified.