The other thing is that many academic department have stipulations in the contract that you cannot moonlight unless you have departmental chair permission. Furthermore, some places will allow you to obtain income via other means (such as consulting, speakiing); however, they have it in your contract that you can only keep X percent of your total salary and anything over that needs to go to the department.
I think that many people that do academics realize that there is less salary involved with it; however, there are other benefits such as being able to help current and future physicians.
Speaking of compensation, I know there have been studies indicating that EM physicians that then do a fellowship tend to get paid less than their non-fellowship trained counterparts. However, this may be a skewed sample as most that have done fellowships will probably be in an academic setting who get paid less than those in community settings.
The other thing that really depends upon your salary is reimbursement. And, many academic centers are in areas where there is a lot of uninsured and underinsured and therefore the reimbursement is much lower.