Sportives you pretend to race
Audax you pretend not to race
Sportives they give you a free gel or a banana
Audax they feed you pasta and cheese rolls.
Sportives give you a number to pin to your jersey
Audax give you a Brevet card to fill in
Sportives give you a timing chip to get round the course as quick as possible
Audax give you a minimum and maximum time of completion
Sportives give you a cheap bit of plastic or metal to hang round your neck saying you have ridden your bike
Audax send you back your brevet card after a few weeks
Sportives you follow some little florescent arrows
Audax you follow a route sheet
Oh yes, and as someone pointed out, about £40 difference.