Oh brother. One can find a group of pessimists to cover any possible need. The good news is that the won't get in the way of those actually doing a thing...
The folks in that thread are talking about capital gains not cash flow - two entirely different views of 'reality'.
None of my income is 'earned'. About half the miles I'll drive my Leaf will be offset by the standard mileage deduction ($0.50/mile for 2010). Over the life of the car that'll be worth much more than the $7500 credit.
When I was on the road selling and delivering long-life synthetic oil and filters, I could have used a small pickup truck and lived with 20mpg. Instead I sold my '96 VW Passat diesel sedan to get a '97 VW Passat TDI station wagon. It would haul 1200 lbs of cargo and return 40mpg at 70-80mph. The car and required 'make ready' maintenance cost $6k. 20,000 to 30,000 miles per year (80% business) returned almost $7K per year from mileage alone. The car was paid for the first year and kept paying me to drive it after that. I really like business deductions and the IRS!
edit... I get that the mileage rate is different from the $7500 EV incentive - just wanted to communicate that there are a number of ways to view the tax 'problem' and that any of us wage earners can choose to play by different rules if we wish, as there are a number of different 'realities' allowed in the tax system.