Hair spray and aerosol deodorant spray (and aerosol sunscreen, too, btw) *ARE* allowed in checked baggage under the toiletries exception to the general aerosol ban.
To qualify as a toiletry so as to be allowed in baggage, the TSA's usual rule of thumb is that the aerosol must be intended for direct application to the surface of the human body. The three most commonly-confiscated items that people lose due to this rule are spray starch, Static Guard spray, and Lysol.
If non-toiletry aerosols are seen they will be confiscated, but apparently the danger is not really severe when small quantities are involved. If it were then TSA folks would be told to actively search for them by opening every checked bag that reveals the outline of a spray can, and right now they don't do that. On beach trips I routinely check a bag that contains upwards of 15 cans of aerosol sunscreen, and I've never had them open it.