Let's see - maybe because I can't buy a UK-spec 520D in the States?
And because a 5 series is a great car (except for the bloody i-Drive), but a totally different class of vehicle in a very different price class?
And maybe because I save about an hour a day driving in the carpool lane? (I didn't ask for it, probably temporary, but loving it while it lasts!)
Maybe because most hybrids do best in stop and go, urban driving - they can maximize electric motor use and get truly sick economy in that environment - and that happens to be the commuting profile I have to deal with.
Open road driving isn't a hybrid strength, though I drove California to Ohio last summer, cruising 80+ mph most of the way, and averaged a tad over 44 mpg, which made me perfectly happy. In any event, Toyota doesn't claim mpg in the 60s in highway driving, which the writers seemed to imply - seems to me the article writers liked the 520 and set it up in its best environment and the Prius' worst. OK, fair enough if you're shopping for an interstate/autobahn burner, but that's NOT the operating environment Toyota designed the Prius for and any intelligent car guy probably knows that already and doesn't need a slanted road test to tell him that. Put a higher-mass 520d into the optimum Prius driving cycle and the results will probably reverse themselves. Different design goals.
And because the Feds gave me a $3100.00 tax credit for purchasing a Prius in 2006?
And because diesel is running about 70 cents a gallon more than 87 octane gas where I live?
And while my family owns a diesel vehicle, a couple of straight gassers, and a Prius, they are different tools for different jobs. I'm a big fan of high technology diesels, and think that they are going to be a huge factor in providing economical, cool vehicles in the US in a few years, but there just aren't a lot of diesel choices right now, especially in California. I'd leap at a 3 series with that 2 liter oilburner if it survives the US emission mods with similar output and economy and the price of diesel comes back to Earth! Meanwhile, the above factors made a hybrid a good choice for me - everybody will have different tradeoffs, but for me, the Prius works. For you, maybe not.