Target Audience AGE...

From the thrillers i've looked at their film certificates are:

• The Usual Suspects (1994) - 18
• Memento (2000) - 15
• Se7en (1996) - 18
  
• Duel (1971) - PG
  
• Speed (1994) - 15
  
• Double Indemnity (1944) - PG
  
• I Walked with a Zombie (1943) - PG
  
• The Bourne Ultimatum (2007) - 12A

Most of the older films were rated PG whereas the newer thrillers are rated between 12A and 18, meaning they are more likely to be viewed by an older audience or ages 12+