I work around the corner from a lab that did research on DVT when it was a hot media issue.
1. DVT are probably a lot more common than is expected. If you go looking for them with ultrasound, a lot of travellers will have them after long flights. But most have no symptoms and resolve with no medication or treatment. Some clots do work loose and end up in nasty places causing problems
2. DVT mainly caused by lack of movement. DVTs have been found in people who sit in front of computer for long periods. The risk of DVT goes up when you get dehydated and blood gets stickier. Gentle leg exercises OK, but actual walking is best.
So, sitting in business class and NOT moving is a risk.
I dont know if the studies have looked in detail at horizontal lie flat beds or jets with communal areas ( A380 bar)
Bring back the Zeppelins
DVICE: New zeppelin designs could reinvigorate airship travel
Design Concept: Strato Cruiser Airship, Floating Along Without Wings or Reality