filmmakers are quite lucky compared to years ago. Today, you can make a movie in just about any format and still be taken seriously, assuming that you have a great story and reasonably good production values. As mentioned, The Blair Witch Project is one of the most successful independent features ever made, yet it was shot with a consumer video camera (non-digital).
Prior to the digital revolution of the 1990s, things were a lot different. If the movie was shot on a format other than 35mm, it did not stand a chance of being distributed. 16mm was not taken seriously and video was a joke. These standards were so ingrained in the industry, that even actors were reluctant to work on non-35mm shoots.
All that has changed now. Affordable, high-quality digital cameras have democratized the industry. Still, 35mm film is the standard by which all video formats are