Wow...you guys could get into a "heated discussion" on this one.....
I am going to stay out of it...but:
1. One theory is pressure...classical.
2. Then there is the source/sink deal (what I learned when going through engr school)....ouch that class was painful...ya know with the rotation and such...
3. Then there is the "what go's up must come down" theory...lol....the amount of air displaced downward equals the lift upward....
4. Then there is the combination....

The bottom line is that the wing does lift...and it follows some equations that model that lift....you throw in some fudge factors here and there derived from test data...and you can calculate the performance of the "thing"...and that is what everyone wants to know...

Steve