Having helped Fortune 150 companies manage these kinds of correspondence before, I will guess that the internal software package that manages the inbound TTU correspondence has some sort of built in SLA (Service Level Agreement) monitoring which auto-esecalates TTU messages based on the scope, catetory and type of issue up the management chain to insure a response within a prescribed timeframe. With e-mail, you lose this monitoring - but it is probably a wash since the e-mail will stand out and demand a response by the very nature it is outside a normal TTU inbound handling queue.

I hope this makes sense...

-A