DVT is not just confined to economy/charter class cabins, SLF travelling in Club/First have also been similarly afflicted. More people get DVT having travelled in Economy than Club/First, but then again more people travel Economy anyway. Has there been any scientific research into the ratios from each cabin, and why if sitting in one place causes DVT are the Flight Crew not dropping like flies.
Seat pitch and general comfort are a separate matter, and generally, as has been said before, you get what you pay for. If you buy a Mini you will not get the same amount of comfort as a Mercedes.