Your personal assets are NOT protected if you do business as a DBA. All the DBA certificate does is let people know who's behind the fictitious name that you created for your company. It does not provide you with any protection from the reach of creditors. You can only get that if you form a corporation, limited liability company, or other limited liability entity . . . AND maintain the annual records and formalities that the law requires of the entity. If you are concerned about protecting your home and personal assets (and if you're in business, you should be), speak to a business attorney.
The fall in new company starts does not necessarily mean that the American economy is less dynamic than it used to be, or that Americans are opening up new establishments at a lower rate than they did in the late 1970s.