Orthognathic Surgery and Trachaeotomy, Normal?

Routine orthognathic surgery may be simple (involving a single jaw) or complex (double jaw).  However, precautionary or routine tracheotomy or crichothyroidotomy is not commonly done or needed.  Severe swelling following surgery is common after orthognathic surgery, which is why most people are admitted to the hospital for 2-3 days to ensure no issues exist with excessive bleeding, pain, or breathing obstruction.  

Protecting your airway post operatively is definitely a priority. You need to talk to your surgeon to understand his thought process. If he is expecting a lot of swelling in the tongue base or throat and you will be having your jaws wired shut then in event of emergency they may not be able to reestablish your airway quick enough to help you. I don't know if this is the thought but you should be able to have it explained to you.

Certainly, you need to maintain a safe airway and I know of one craniofacial surgeon who did traceostomies at the time of surgery if he was also doing an extensive cleft lip rhinoplasty along with the orthognathic surgery but your surgery sound like maybe less airway compromise.  If you are uncomfortable, see some other doctors.