Do all employers have to offer health care to their employees?

No. Only large employers will face penalties for not providing insurance to employees. Under the new ACA law, small businesses with less than 50 employees are exempt from the penalty for not offering coverage to their employees.
Small businesses that do offer insurance to its employees may qualify for a tax credit as an incentive.
For companies with at least 50 employees, there are penalties if the business does not offer health insurance.