Tricky questions.
The DVT issue is primarily as a result of media hype. The "problem" has been around for years but due to media interest has been catapulted into the public eye. Susceptibility would appear to be a contributing factor: support stockings, minimal alcohol intake, plenty of water and some simple exercises help to reduce the risk.
Passenger expectation is, as Affirm says, based on the failure of airlines to represent economy class travel accurately. The glossy ads generally show business or first to highlight the level of service and comfort but the pricing ads quote the lowest fares in economy. Hence the disparity between expectation (what,s in the glossy,s] and reality - whats you get for £29 in economy.
Most pax know that the time in the tube is more or less fixed: you can get to JFk in 7 hours or 6 hours 50 - what,s 10 mins in 7 hours? But the real time savings can be made on the ground prior to and after flight. Improved boarding and check in so that hanging about is minimised: improved disembarkation and baggage recovery at the other end.
Problem there is that the airports rely on pax hanging about pre flight and spending money in the cafes, bars and shops. Also they want the waiting friends etc to the same at the destination, hence improving things isn,t really in their interest.