I can confirm the 33mpg+ (7L/100km) combined, highway is easily 47mpg (5L/100km) to as high, in some cases even low 50's mpg is seen (My best was 53mpg 4.54L/100km going down to Florida fully loaded above the speed limit a good bit. My best in the '98 was 61mpg 3.85L/100km Boston to Toronto with some city thrown in at the end) . However your typical mileage per year estimate is a little low per year. Typically the serious TDI owners will do at least 25,000miles per year or more. I averaged that amount on the '09 and from a service and initial cost point I was just past the break even point. My previous '98 TDI I was closer to the 40,000 mile point at which time the saving really start to show.
Add into the equation to get the higher mileage it is usually highway and as a result better economy.
Based on my experience 25 to 30,000miles year is the point you should consider diesel, anything less gas is likely to your advantage both. I suspect some of my diesel issues were do to the fact that it was relatively low mileage (ie turbo failure).
This are distance drive cars, not city cars.
Another bit of history the original TDI's were run rich (compared to the Euro spec cars) to reduce combustion temps to reduce the NO2 production, this also reduced the horse power and increase fuel usage. Back in those days lean it out solved both problems but increased NO2 production.....Fuel usage decreased by 10%, do that to the current cars, 10% will still give good performance while still giving good mileage.