I thought the store front provision was a state or local requirement. Some gun shops around here flat out refuse to receive "in production" guns. I can't understand that as they can charge as much for the handling fee as they would profit from the sale of a new gun.
Several years ago, I believe it was during the late 90's, the Feds decided that too many people were operating out of their homes and making some questionable sales. To eliminate the amount of firearm dealers, they wrote into the rules that an actual storefront was required before a license could be obtained.
I am not sure if that rule still holds or if it has been done away with. The government changes the rules as they see fit.
On Edit: I found the rule still holds. Here is what is said about licensing requirements.
Now before you fill out your application, there a few basic requirements that the Bureau of Alcohol, Tobacco, Firearms and Explosives says you must meet in order to become licensed. These are as follows:
The first is that you're 21 years of age or older.
The second is that you're not prohibited from possessing firearms.
The third is that you haven't violated any regulations of the Gun Control Act.
The fourth is that you can't lie on your application, or fail to disclose information on it.
The fifth is that you have an approved location or premises that will be used for conducting business or for your gun collection.
Furthermore, once you've met those requirements, you'll also be required to confirm that:
Any business that you're intending to conduct at the licensed location is not prohibited under any state or local laws.
That you'll comply with any local or state laws that may pertain to your business within 30 days of approval of your license.
That you will not do any business until such time as you have met all of the local and state laws that pertain to your business.
You must notify your local Chief of Police via a form, that you intend to apply for a license, and where the licensed location will be.
And finally, you'll need to provide some type of secure storage and safety devices for any firearms that are sold at your location.