Forgive my ignorance but considering the amount of flights per day and the thousands and thousands of people on them at all times it would seem to me that the actual odds of suffering from DVT or some embolism from flying is about the same as getting struck by lightening. I fly a lot for my job, often half way around the world, so i would be interested to see some hard statistics on how many serious cases happen per year and also how many of these people are generally unhealthy, smokers, elderly or over weight... Just curious.
Fontaine
You have a point; but I think the take home message here is that DVT can happen to anyone and can be serious or even fatal.
DVT is one of those things that has a number of predisposing causes - if you have the risk factors, overweight, smoker, birth control pills etc (and even if you don't) and then you expose yourself to one of these predisposing causes, like flying, you can get a DVT, whereas otherwise you would not get it. So it is in fact mostly preventable. There are definitely more DVT's than people getting struck by lightning. There is conflicting evidence on the number of DVT's related to flying, ranging from some who say it's unrelated to those who say as many as 10% of fliers would have a detectable DVT if one were to ultrasound everyone's legs. The answer is probably somewhere in the middle. DVT's are frequently asymptomatic, so people may get them, and not know they have them. If they are small enough, they probably dissolve over time and no big deal. On the other hand the first time a DVT is diagnosed is often when someone is hospitalized or dies from a pulmonary embolism.
The important points to remember are that if you are one of the few unlucky people who get a DVT, it is a real PITA from a treatment standpoint having to be on anticoagulants, you are at increased risk for it happening again, and most importantly if a piece of the clot breaks off and you get a pulmonary embolism, the fatality rate is very high, especially if you are not close to a hospital. The chairman of my surgery program died from a pulmonary embolism - he was older but otherwise healthy and a non-smoker and not overweight, and did not have symptoms of a DVT, or at least did not recognize them. So yes, you can die from a DVT!
To me, it's about things that are easily preventable, like wearing compression socks or just doing some exercises even while in the chair. Some airlines even have suggest exercises in the video console. Anyone who flies a lot, the chances rise accordingly. Then again, with the radiation exposure, DVT, carbon footprint and TSA/immigration, I wonder why I bother flying so much! 
