There is nothing wrong with an emailed tune. At the end of the day it is still a data file that controls the parameters of your car. However, not all tunes and tuners are equal.
Some people have had great success with BAMA, and others have experienced problems. The same can be said for Steeda or anyone else that is writing a tune.
The benefit to a dyno tune is in the thought that every last ounce of power can be found and applied. I will agree that you will get a very accurate tune specific to your needs while using a dyno, but even a dyno is not perfect.
When you put your car in front of a fan, and set its wheels on the rollers, your first pull is a data log that applies to the environment the dyno is in. Your tech / tuner is tuning for the optimum results at that point in time. Your car will have the hood up, so you will be getting better air flow than normal. You will also have less overall heat due to the open hood. Ambient air temp, barometric pressure, humidity, altitude, etc is all a part of the dyno's environment, and plays a part in the final result.
So how do the emailed tunes get the job done? Normally the people writing the tunes have a conservative set of parameters to follow that were applied to various other cars like yours, with the same modifications. The data is collected through dyno run sheets, and real time data logs.
If you have a tunes for life program, you should be able to run a real time, street data log, and have the tuner adjust the parameters as accurate, if not more accurate than on a dyno. The truth is that a "canned" tune is basically an educated guess.
While I was racing drag bikes, I never put my bike on a dyno. I would run a test pass, get the data log, and then adjust the timing, air/fuel ratio, etc given my location and conditions. There is not a need to be this accurate with a daily driven street vehicle. If you are pushing for every ounce of power possible, I can promise you that something will break while you push the limits.
Long answer short; an email tune is fine more times than not.