I have a gmail account with a name that you can probably guess. There are many other people in the world with my name. It is very easy for somebody trying to email another Sean McGrath to e-mail me on gmail by mistake. Over the last while I have received 2-3 of these.
With company-centric e-mail addresses, you have to be more unlucky to send an e-mail to the wrong person. With gmail, pretty much every common name you can think off is registered to someone, somewhere @gmail.com. Therefore, the positive feedback associated with a bouncing e-mail - the loud and clear "No such person at that address buddy", doesn't happen with gmail.