Don't know if this is because I am using IMAP to connect to gmail so it doesn't really see them (but seems to work with other pictures emailed to me) or whether it is due to the iPhone 'embedding' the images rather than attaching them?
Photos sent as true attachments to the message are not embedded with the iPhone's Mail client. Photos sent as true attachments are displayed inline or viewed in place within the body of the message, which is not the same as being embedded.
Doing this with an email client on your computer, there should be nothing special or different with the photos emailed by your iPhone with your Gmail account. I regularly send photos with my MobileMe account from my iPhone, and I can save the photos sent with my MobileMe account from the account's server stored Sent mailbox with the Mail.app on my Mac. I haven't tried to save all photos sent from every sent message in my account's Sent mailbox in bulk, but the photos are sent as true attachments to the message.