The only difference between shooting and snorting seems to be the average particle sizes observed in the lungs of the user. This observation has been made by many different groups that study talc induced granulomas and other similar diseases, but is not fully understood.
People seem to have the impression that snorting is safer than shooting, it's not. It's been known since the early 70's that both routes introduce talc into the lungs. Once it's in there, your body (mostly macrophages) will try to engulf it to get rid of it. This leads to several diseases/conditions such as granulomatosis, precocious emphysema, fibrosis, etc.
It's actually fairly easy to see talc in a lung, assuming you have a bronchiolar lavage sample. Talc is birefringent and easily observed under a scope. The longer the particle has been in the lung, the larger it will get as cells try to attack it (usually). The body recognizes it as being foreign easily and knows it shouldn't be in the lung. There have even been cases attributed to inhalation of baby powder (not intentional) as well as occupational inhalation.
Also, it's not only talc microcrystalline cellulose, cornstarch and silicates are just as responsible. There have even been cases where the talc exposure was attributed to cocaine inhalation- it was a known coke user who didn't inject. The case report mentioned that they did look for signs of injection and none were found. The guy did admit to snorting it though.
***Note for the most part, I am talking about crushed pharmaceuticals in the above- with the exception of the cocaine example.